Provided by: gmt-common_5.2.1+dfsg-3build1_all 
NAME
gmtmath - Reverse Polish Notation (RPN) calculator for data tables
SYNOPSIS
gmtmath [ t_f(t).d[+e][+s|w] ] [ cols ] [ eigen ] [ ] [ n_col[/t_col] ] [ ] [ [f|l] ] [
t_min/t_max/t_inc[+]|tfile ] [ [level] ] [ -b<binary> ] [ -d<nodata> ] [ -f<flags> ] [ -g<gaps> ] [
-h<headers> ] [ -i<flags> ] [ -o<flags> ] [ -s<flags> ] operand [ operand ] OPERATOR [ operand ] OPERATOR
... = [ outfile ]
Note: No space is allowed between the option flag and the associated arguments.
DESCRIPTION
gmtmath will perform operations like add, subtract, multiply, and divide on one or more table data files
or constants using Reverse Polish Notation (RPN) syntax (e.g., Hewlett-Packard calculator-style).
Arbitrarily complicated expressions may therefore be evaluated; the final result is written to an output
file [or standard output]. Data operations are element-by-element, not matrix manipulations (except where
noted). Some operators only require one operand (see below). If no data tables are used in the expression
then options -T, -N can be set (and optionally -bo to indicate the data type for binary tables). If STDIN
is given, the standard input will be read and placed on the stack as if a file with that content had been
given on the command line. By default, all columns except the "time" column are operated on, but this can
be changed (see -C). Complicated or frequently occurring expressions may be coded as a macro for future
use or stored and recalled via named memory locations.
REQUIRED ARGUMENTS
operand
If operand can be opened as a file it will be read as an ASCII (or binary, see -bi) table data
file. If not a file, it is interpreted as a numerical constant or a special symbol (see below).
The special argument STDIN means that stdin will be read and placed on the stack; STDIN can appear
more than once if necessary.
outfile
The name of a table data file that will hold the final result. If not given then the output is
sent to stdout.
OPTIONAL ARGUMENTS
-At_f(t).d[+e][+s|w]
Requires -N and will partially initialize a table with values from the given file containing t and
f(t) only. The t is placed in column t_col while f(t) goes into column n_col - 1 (see -N). If
used with operators LSQFIT and SVDFIT you can optionally append the modifier +e which will instead
evaluate the solution and write a data set with four columns: t, f(t), the model solution at t,
and the the residuals at t, respectively [Default writes one column with model coefficients].
Append +w if t_f(t).d has a third column with weights, or append +s if t_f(t).d has a third column
with 1-sigma. In those two cases we find the weighted solution. The weights (or sigmas) will be
output as the last column when +e is in effect.
-Ccols Select the columns that will be operated on until next occurrence of -C. List columns separated by
commas; ranges like 1,3-5,7 are allowed. -C (no arguments) resets the default action of using all
columns except time column (see -N). -Ca selects all columns, including time column, while -Cr
reverses (toggles) the current choices. When -C is in effect it also controls which columns from
a file will be placed on the stack.
-Eeigen
Sets the minimum eigenvalue used by operators LSQFIT and SVDFIT [1e-7]. Smaller eigenvalues are
set to zero and will not be considered in the solution.
-I Reverses the output row sequence from ascending time to descending [ascending].
-Nn_col[/t_col]
Select the number of columns and optionally the column number that contains the "time" variable
[0]. Columns are numbered starting at 0 [2/0]. If input files are specified then -N will add any
missing columns.
-Q Quick mode for scalar calculation. Shorthand for -Ca -N1/0 -T0/0/1.
-S[f|l]
Only report the first or last row of the results [Default is all rows]. This is useful if you have
computed a statistic (say the MODE) and only want to report a single number instead of numerous
records with identical values. Append l to get the last row and f to get the first row only
[Default].
-Tt_min/t_max/t_inc[+]|tfile
Required when no input files are given. Sets the t-coordinates of the first and last point and the
equidistant sampling interval for the "time" column (see -N). Append + if you are specifying the
number of equidistant points instead. If there is no time column (only data columns), give -T with
no arguments; this also implies -Ca. Alternatively, give the name of a file whose first column
contains the desired t-coordinates which may be irregular.
-V[level] (more ...)
Select verbosity level [c].
-bi[ncols][t] (more ...)
Select native binary input.
-bo[ncols][type] (more ...)
Select native binary output. [Default is same as input, but see -o]
-d[i|o]nodata (more ...)
Replace input columns that equal nodata with NaN and do the reverse on output.
-f[i|o]colinfo (more ...)
Specify data types of input and/or output columns.
-g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (more ...)
Determine data gaps and line breaks.
-h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
Skip or produce header record(s).
-icols[l][sscale][ooffset][,...] (more ...)
Select input columns (0 is first column).
-ocols[,...] (more ...)
Select output columns (0 is first column).
-s[cols][a|r] (more ...)
Set handling of NaN records.
-^ or just -
Print a short message about the syntax of the command, then exits (NOTE: on Windows use just -).
-+ or just +
Print an extensive usage (help) message, including the explanation of any module-specific option
(but not the GMT common options), then exits.
-? or no arguments
Print a complete usage (help) message, including the explanation of options, then exits.
--version
Print GMT version and exit.
--show-datadir
Print full path to GMT share directory and exit.
OPERATORS
Choose among the following 146 operators. "args" are the number of input and output arguments.
───────────────────────────────────────────────────
Operator args Returns
───────────────────────────────────────────────────
ABS 1 1 abs (A)
───────────────────────────────────────────────────
ACOS 1 1 acos (A)
───────────────────────────────────────────────────
ACOSH 1 1 acosh (A)
───────────────────────────────────────────────────
ACSC 1 1 acsc (A)
───────────────────────────────────────────────────
ACOT 1 1 acot (A)
───────────────────────────────────────────────────
ADD 2 1 A + B
───────────────────────────────────────────────────
AND 2 1 B if A == NaN, else A
───────────────────────────────────────────────────
ASEC 1 1 asec (A)
───────────────────────────────────────────────────
ASIN 1 1 asin (A)
───────────────────────────────────────────────────
ASINH 1 1 asinh (A)
───────────────────────────────────────────────────
ATAN 1 1 atan (A)
───────────────────────────────────────────────────
ATAN2 2 1 atan2 (A, B)
───────────────────────────────────────────────────
ATANH 1 1 atanh (A)
───────────────────────────────────────────────────
BCDF 3 1 Binomial cumulative
distribution function for p
= A, n = B, and x = C
───────────────────────────────────────────────────
BPDF 3 1 Binomial probability density
function for p = A, n = B,
and x = C
───────────────────────────────────────────────────
BEI 1 1 bei (A)
───────────────────────────────────────────────────
BER 1 1 ber (A)
───────────────────────────────────────────────────
BITAND 2 1 A & B (bitwise AND operator)
───────────────────────────────────────────────────
BITLEFT 2 1 A << B (bitwise left-shift
operator)
───────────────────────────────────────────────────
BITNOT 1 1 ~A (bitwise NOT operator,
i.e., return two's
complement)
───────────────────────────────────────────────────
BITOR 2 1 A | B (bitwise OR operator)
───────────────────────────────────────────────────
BITRIGHT 2 1 A >> B (bitwise right-shift
operator)
───────────────────────────────────────────────────
BITTEST 2 1 1 if bit B of A is set, else
0 (bitwise TEST operator)
───────────────────────────────────────────────────
BITXOR 2 1 A ^ B (bitwise XOR operator)
───────────────────────────────────────────────────
CEIL 1 1 ceil (A) (smallest integer
>= A)
───────────────────────────────────────────────────
CHICRIT 2 1 Chi-squared distribution
critical value for alpha = A
and nu = B
───────────────────────────────────────────────────
CHICDF 2 1 Chi-squared cumulative
distribution function for
chi2 = A and nu = B
───────────────────────────────────────────────────
CHIPDF 2 1 Chi-squared probability
density function for chi2 =
A and nu = B
───────────────────────────────────────────────────
COL 1 1 Places column A on the stack
───────────────────────────────────────────────────
COMB 2 1 Combinations n_C_r, with n =
A and r = B
───────────────────────────────────────────────────
CORRCOEFF 2 1 Correlation coefficient r(A,
B)
───────────────────────────────────────────────────
COS 1 1 cos (A) (A in radians)
───────────────────────────────────────────────────
COSD 1 1 cos (A) (A in degrees)
───────────────────────────────────────────────────
COSH 1 1 cosh (A)
───────────────────────────────────────────────────
COT 1 1 cot (A) (A in radians)
───────────────────────────────────────────────────
COTD 1 1 cot (A) (A in degrees)
───────────────────────────────────────────────────
CSC 1 1 csc (A) (A in radians)
───────────────────────────────────────────────────
CSCD 1 1 csc (A) (A in degrees)
───────────────────────────────────────────────────
DDT 1 1 d(A)/dt Central 1st
derivative
───────────────────────────────────────────────────
D2DT2 1 1 d^2(A)/dt^2 2nd derivative
───────────────────────────────────────────────────
D2R 1 1 Converts Degrees to Radians
───────────────────────────────────────────────────
DENAN 2 1 Replace NaNs in A with
values from B
───────────────────────────────────────────────────
DILOG 1 1 dilog (A)
───────────────────────────────────────────────────
DIFF 1 1 Difference between adjacent
elements of A (A[1]-A[0],
A[2]-A[1], ..., 0)
───────────────────────────────────────────────────
DIV 2 1 A / B
───────────────────────────────────────────────────
DUP 1 2 Places duplicate of A on the
stack
───────────────────────────────────────────────────
ECDF 2 1 Exponential cumulative
distribution function for x
= A and lambda = B
───────────────────────────────────────────────────
ECRIT 2 1 Exponential distribution
critical value for alpha = A
and lambda = B
───────────────────────────────────────────────────
EPDF 2 1 Exponential probability
density function for x = A
and lambda = B
───────────────────────────────────────────────────
ERF 1 1 Error function erf (A)
───────────────────────────────────────────────────
ERFC 1 1 Complementary Error function
erfc (A)
───────────────────────────────────────────────────
ERFINV 1 1 Inverse error function of A
───────────────────────────────────────────────────
EQ 2 1 1 if A == B, else 0
───────────────────────────────────────────────────
EXCH 2 2 Exchanges A and B on the
stack
───────────────────────────────────────────────────
EXP 1 1 exp (A)
───────────────────────────────────────────────────
FACT 1 1 A! (A factorial)
───────────────────────────────────────────────────
FCDF 3 1 F cumulative distribution
function for F = A, nu1 = B,
and nu2 = C
───────────────────────────────────────────────────
FCRIT 3 1 F distribution critical
value for alpha = A, nu1 =
B, and nu2 = C
───────────────────────────────────────────────────
FLIPUD 1 1 Reverse order of each column
───────────────────────────────────────────────────
FLOOR 1 1 floor (A) (greatest integer
<= A)
───────────────────────────────────────────────────
FMOD 2 1 A % B (remainder after
truncated division)
───────────────────────────────────────────────────
FPDF 3 1 F probability density
function for F = A, nu1 = B,
and nu2 = C
───────────────────────────────────────────────────
GE 2 1 1 if A >= B, else 0
───────────────────────────────────────────────────
GT 2 1 1 if A > B, else 0
───────────────────────────────────────────────────
HYPOT 2 1 hypot (A, B) = sqrt (A*A +
B*B)
───────────────────────────────────────────────────
I0 1 1 Modified Bessel function of
A (1st kind, order 0)
───────────────────────────────────────────────────
I1 1 1 Modified Bessel function of
A (1st kind, order 1)
───────────────────────────────────────────────────
IFELSE 3 1 B if A != 0, else C
───────────────────────────────────────────────────
IN 2 1 Modified Bessel function of
A (1st kind, order B)
───────────────────────────────────────────────────
INRANGE 3 1 1 if B <= A <= C, else 0
───────────────────────────────────────────────────
INT 1 1 Numerically integrate A
───────────────────────────────────────────────────
INV 1 1 1 / A
───────────────────────────────────────────────────
ISFINITE 1 1 1 if A is finite, else 0
───────────────────────────────────────────────────
ISNAN 1 1 1 if A == NaN, else 0
───────────────────────────────────────────────────
J0 1 1 Bessel function of A (1st
kind, order 0)
───────────────────────────────────────────────────
J1 1 1 Bessel function of A (1st
kind, order 1)
───────────────────────────────────────────────────
JN 2 1 Bessel function of A (1st
kind, order B)
───────────────────────────────────────────────────
K0 1 1 Modified Kelvin function of
A (2nd kind, order 0)
───────────────────────────────────────────────────
K1 1 1 Modified Bessel function of
A (2nd kind, order 1)
───────────────────────────────────────────────────
KN 2 1 Modified Bessel function of
A (2nd kind, order B)
───────────────────────────────────────────────────
KEI 1 1 kei (A)
───────────────────────────────────────────────────
KER 1 1 ker (A)
───────────────────────────────────────────────────
KURT 1 1 Kurtosis of A
───────────────────────────────────────────────────
LCDF 1 1 Laplace cumulative
distribution function for z
= A
───────────────────────────────────────────────────
LCRIT 1 1 Laplace distribution
critical value for alpha = A
───────────────────────────────────────────────────
LE 2 1 1 if A <= B, else 0
───────────────────────────────────────────────────
LMSSCL 1 1 LMS scale estimate (LMS STD)
of A
───────────────────────────────────────────────────
LOG 1 1 log (A) (natural log)
───────────────────────────────────────────────────
LOG10 1 1 log10 (A) (base 10)
───────────────────────────────────────────────────
LOG1P 1 1 log (1+A) (accurate for
small A)
───────────────────────────────────────────────────
LOG2 1 1 log2 (A) (base 2)
───────────────────────────────────────────────────
LOWER 1 1 The lowest (minimum) value
of A
───────────────────────────────────────────────────
LPDF 1 1 Laplace probability density
function for z = A
───────────────────────────────────────────────────
LRAND 2 1 Laplace random noise with
mean A and std. deviation B
───────────────────────────────────────────────────
LSQFIT 1 0 Let current table be [A | b]
return least squares
solution x = A \ b
───────────────────────────────────────────────────
LT 2 1 1 if A < B, else 0
───────────────────────────────────────────────────
MAD 1 1 Median Absolute Deviation
(L1 STD) of A
───────────────────────────────────────────────────
MAX 2 1 Maximum of A and B
───────────────────────────────────────────────────
MEAN 1 1 Mean value of A
───────────────────────────────────────────────────
MED 1 1 Median value of A
───────────────────────────────────────────────────
MIN 2 1 Minimum of A and B
───────────────────────────────────────────────────
MOD 2 1 A mod B (remainder after
floored division)
───────────────────────────────────────────────────
MODE 1 1 Mode value (Least Median of
Squares) of A
───────────────────────────────────────────────────
MUL 2 1 A * B
───────────────────────────────────────────────────
NAN 2 1 NaN if A == B, else A
───────────────────────────────────────────────────
NEG 1 1 -A
───────────────────────────────────────────────────
NEQ 2 1 1 if A != B, else 0
───────────────────────────────────────────────────
NORM 1 1 Normalize (A) so
max(A)-min(A) = 1
───────────────────────────────────────────────────
NOT 1 1 NaN if A == NaN, 1 if A ==
0, else 0
───────────────────────────────────────────────────
NRAND 2 1 Normal, random values with
mean A and std. deviation B
───────────────────────────────────────────────────
OR 2 1 NaN if B == NaN, else A
───────────────────────────────────────────────────
PCDF 2 1 Poisson cumulative
distribution function for x
= A and lambda = B
───────────────────────────────────────────────────
PERM 2 1 Permutations n_P_r, with n =
A and r = B
───────────────────────────────────────────────────
PPDF 2 1 Poisson distribution
P(x,lambda), with x = A and
lambda = B
───────────────────────────────────────────────────
PLM 3 1 Associated Legendre
polynomial P(A) degree B
order C
───────────────────────────────────────────────────
PLMg 3 1 Normalized associated
Legendre polynomial P(A)
degree B order C
(geophysical convention)
───────────────────────────────────────────────────
POP 1 0 Delete top element from the
stack
───────────────────────────────────────────────────
POW 2 1 A ^ B
───────────────────────────────────────────────────
PQUANT 2 1 The B'th Quantile (0-100%)
of A
───────────────────────────────────────────────────
PSI 1 1 Psi (or Digamma) of A
───────────────────────────────────────────────────
PV 3 1 Legendre function Pv(A) of
degree v = real(B) + imag(C)
───────────────────────────────────────────────────
QV 3 1 Legendre function Qv(A) of
degree v = real(B) + imag(C)
───────────────────────────────────────────────────
R2 2 1 R2 = A^2 + B^2
───────────────────────────────────────────────────
R2D 1 1 Convert Radians to Degrees
───────────────────────────────────────────────────
RAND 2 1 Uniform random values
between A and B
───────────────────────────────────────────────────
RCDF 1 1 Rayleigh cumulative
distribution function for z
= A
───────────────────────────────────────────────────
RCRIT 1 1 Rayleigh distribution
critical value for alpha = A
───────────────────────────────────────────────────
RINT 1 1 rint (A) (round to integral
value nearest to A)
───────────────────────────────────────────────────
RPDF 1 1 Rayleigh probability density
function for z = A
───────────────────────────────────────────────────
ROLL 2 0 Cyclicly shifts the top A
stack items by an amount B
───────────────────────────────────────────────────
ROTT 2 1 Rotate A by the (constant)
shift B in the t-direction
───────────────────────────────────────────────────
SEC 1 1 sec (A) (A in radians)
───────────────────────────────────────────────────
SECD 1 1 sec (A) (A in degrees)
───────────────────────────────────────────────────
SIGN 1 1 sign (+1 or -1) of A
───────────────────────────────────────────────────
SIN 1 1 sin (A) (A in radians)
───────────────────────────────────────────────────
SINC 1 1 sinc (A) (sin (pi*A)/(pi*A))
───────────────────────────────────────────────────
SIND 1 1 sin (A) (A in degrees)
───────────────────────────────────────────────────
SINH 1 1 sinh (A)
───────────────────────────────────────────────────
SKEW 1 1 Skewness of A
───────────────────────────────────────────────────
SQR 1 1 A^2
───────────────────────────────────────────────────
SQRT 1 1 sqrt (A)
───────────────────────────────────────────────────
STD 1 1 Standard deviation of A
───────────────────────────────────────────────────
STEP 1 1 Heaviside step function H(A)
───────────────────────────────────────────────────
STEPT 1 1 Heaviside step function
H(t-A)
───────────────────────────────────────────────────
SUB 2 1 A - B
───────────────────────────────────────────────────
SUM 1 1 Cumulative sum of A
───────────────────────────────────────────────────
TAN 1 1 tan (A) (A in radians)
───────────────────────────────────────────────────
TAND 1 1 tan (A) (A in degrees)
───────────────────────────────────────────────────
TANH 1 1 tanh (A)
───────────────────────────────────────────────────
TAPER 1 1 Unit weights cosine-tapered
to zero within A of end
margins
───────────────────────────────────────────────────
TN 2 1 Chebyshev polynomial
Tn(-1<A<+1) of degree B
───────────────────────────────────────────────────
TCRIT 2 1 Student's t distribution
critical value for alpha = A
and nu = B
───────────────────────────────────────────────────
TPDF 2 1 Student's t probability
density function for t = A,
and nu = B
───────────────────────────────────────────────────
TCDF 2 1 Student's t cumulative
distribution function for t
= A, and nu = B
───────────────────────────────────────────────────
UPPER 1 1 The highest (maximum) value
of A
───────────────────────────────────────────────────
WCDF 3 1 Weibull cumulative
distribution function for x
= A, scale = B, and shape =
C
───────────────────────────────────────────────────
WCRIT 3 1 Weibull distribution
critical value for alpha =
A, scale = B, and shape = C
───────────────────────────────────────────────────
WPDF 3 1 Weibull density distribution
P(x,scale,shape), with x =
A, scale = B, and shape = C
───────────────────────────────────────────────────
XOR 2 1 B if A == NaN, else A
───────────────────────────────────────────────────
Y0 1 1 Bessel function of A (2nd
kind, order 0)
───────────────────────────────────────────────────
Y1 1 1 Bessel function of A (2nd
kind, order 1)
───────────────────────────────────────────────────
YN 2 1 Bessel function of A (2nd
kind, order B)
───────────────────────────────────────────────────
ZCDF 1 1 Normal cumulative
distribution function for z
= A
───────────────────────────────────────────────────
ZPDF 1 1 Normal probability density
function for z = A
───────────────────────────────────────────────────
ZCRIT 1 1 Normal distribution critical
value for alpha = A
───────────────────────────────────────────────────
ROOTS 2 1 Treats col A as f(t) = 0 and
returns its roots
┌───────────┬──────┬──────────────────────────────┐
│ │ │ │
SYMBOLS │ │ │ │
--
ASCII FORMAT PRECISION │ │ │ │
--
NOTES ON OPERATORS
1. The operators PLM and PLMg calculate the associated Legendre polynomial of degree L and order M in x
which must satisfy -1 <= x <= +1 and 0 <= M <= L. x, L, and M are the three arguments preceding the
operator. PLM is not normalized and includes the Condon-Shortley phase (-1)^M. PLMg is normalized in the
way that is most commonly used in geophysics. The C-S phase can be added by using -M as argument. PLM
will overflow at higher degrees, whereas PLMg is stable until ultra high degrees (at least 3000).
2. Files that have the same names as some operators, e.g., ADD, SIGN, =, etc. should be identified by
prepending the current directory (i.e., ./).
3. The stack depth limit is hard-wired to 100.
4. All functions expecting a positive radius (e.g., LOG, KEI, etc.) are passed the absolute value of
their argument.
5. The DDT and D2DT2 functions only work on regularly spaced data.
6. All derivatives are based on central finite differences, with natural boundary conditions.
7. ROOTS must be the last operator on the stack, only followed by =.
STORE, RECALL AND CLEAR
You may store intermediate calculations to a named variable that you may recall and place on the stack at
a later time. This is useful if you need access to a computed quantity many times in your expression as
it will shorten the overall expression and improve readability. To save a result you use the special
operator STO@label, where label is the name you choose to give the quantity. To recall the stored result
to the stack at a later time, use [RCL]@label, i.e., RCL is optional. To clear memory you may use
CLR@label. Note that STO and CLR leave the stack unchanged.
8. The bitwise operators (BITAND, BITLEFT, BITNOT, BITOR, BITRIGHT, BITTEST, and BITXOR) convert a
tables's double precision values to unsigned 64-bit ints to perform the bitwise operations. Consequently,
the largest whole integer value that can be stored in a double precision value is 2^53 or
9,007,199,254,740,992. Any higher result will be masked to fit in the lower 54 bits. Thus, bit
operations are effectively limited to 54 bits. All bitwise operators return NaN if given NaN arguments
or bit-settings <= 0.
9. TAPER will interpret its argument to be a width in the same units as the time-axis, but if no time is
provided (i.e., plain data tables) then the width is taken to be given in number of rows.
MACROS
Users may save their favorite operator combinations as macros via the file gmtmath.macros in their
current or user directory. The file may contain any number of macros (one per record); comment lines
starting with # are skipped. The format for the macros is name = arg1 arg2 ... arg2 [ : comment] where
name is how the macro will be used. When this operator appears on the command line we simply replace it
with the listed argument list. No macro may call another macro. As an example, the following macro
expects that the time-column contains seafloor ages in Myr and computes the predicted half-space
bathymetry:
DEPTH = SQRT 350 MUL 2500 ADD NEG : usage: DEPTH to return half-space seafloor depths
Note: Because geographic or time constants may be present in a macro, it is required that the optional
comment flag (:) must be followed by a space. As another example, we show a macro GPSWEEK which
determines which GPS week a timestamp belongs to:
GPSWEEK = 1980-01-06T00:00:00 SUB 86400 DIV 7 DIV FLOOR : GPS week without rollover
EXAMPLES
To take the square root of the content of the second data column being piped through gmtmath by process1
and pipe it through a 3rd process, use
process1 | gmt math STDIN SQRT = | process3
To take log10 of the average of 2 data files, use
gmt math file1.d file2.d ADD 0.5 MUL LOG10 = file3.d
Given the file samples.d, which holds seafloor ages in m.y. and seafloor depth in m, use the relation
depth(in m) = 2500 + 350 * sqrt (age) to print the depth anomalies:
gmt math samples.d T SQRT 350 MUL 2500 ADD SUB = | lpr
To take the average of columns 1 and 4-6 in the three data sets sizes.1, sizes.2, and sizes.3, use
gmt math -C1,4-6 sizes.1 sizes.2 ADD sizes.3 ADD 3 DIV = ave.d
To take the 1-column data set ages.d and calculate the modal value and assign it to a variable, try
gmt set mode_age = `gmt math -S -T ages.d MODE =`
To evaluate the dilog(x) function for coordinates given in the file t.d:
gmt math -Tt.d T DILOG = dilog.d
To demonstrate the use of stored variables, consider this sum of the first 3 cosine harmonics where we
store and repeatedly recall the trigonometric argument (2*pi*T/360):
gmt math -T0/360/1 2 PI MUL 360 DIV T MUL STO@kT COS @kT 2 MUL COS ADD \
@kT 3 MUL COS ADD = harmonics.d
To use gmtmath as a RPN Hewlett-Packard calculator on scalars (i.e., no input files) and calculate
arbitrary expressions, use the -Q option. As an example, we will calculate the value of Kei (((1 +
1.75)/2.2) + cos (60)) and store the result in the shell variable z:
set z = `gmt math -Q 1 1.75 ADD 2.2 DIV 60 COSD ADD KEI =`
To use gmtmath as a general least squares equation solver, imagine that the current table is the
augmented matrix [ A | b ] and you want the least squares solution x to the matrix equation A * x = b.
The operator LSQFIT does this; it is your job to populate the matrix correctly first. The -A option will
facilitate this. Suppose you have a 2-column file ty.d with t and b(t) and you would like to fit a the
model y(t) = a + b*t + c*H(t-t0), where H is the Heaviside step function for a given t0 = 1.55. Then, you
need a 4-column augmented table loaded with t in column 1 and your observed y(t) in column 3. The
calculation becomes
gmt math -N4/1 -Aty.d -C0 1 ADD -C2 1.55 STEPT ADD -Ca LSQFIT = solution.d
Note we use the -C option to select which columns we are working on, then make active all the columns we
need (here all of them, with -Ca) before calling LSQFIT. The second and fourth columns (col numbers 1 and
3) are preloaded with t and y(t), respectively, the other columns are zero. If you already have a
pre-calculated table with the augmented matrix [ A | b ] in a file (say lsqsys.d), the least squares
solution is simply
gmt math -T lsqsys.d LSQFIT = solution.d
Users must be aware that when -C controls which columns are to be active the control extends to placing
columns from files as well. Contrast the different result obtained by these very similar commands:
echo 1 2 3 4 | gmt math STDIN -C3 1 ADD =
1 2 3 5
versus
echo 1 2 3 4 | gmt math -C3 STDIN 1 ADD =
0 0 0 5
REFERENCES
Abramowitz, M., and I. A. Stegun, 1964, Handbook of Mathematical Functions, Applied Mathematics Series,
vol. 55, Dover, New York.
Holmes, S. A., and W. E. Featherstone, 2002, A unified approach to the Clenshaw summation and the
recursive computation of very high degree and order normalized associated Legendre functions. Journal of
Geodesy, 76, 279-299.
Press, W. H., S. A. Teukolsky, W. T. Vetterling, and B. P. Flannery, 1992, Numerical Recipes, 2nd
edition, Cambridge Univ., New York.
Spanier, J., and K. B. Oldman, 1987, An Atlas of Functions, Hemisphere Publishing Corp.
SEE ALSO
gmt, grdmath
COPYRIGHT
2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.2.1 January 28, 2016 GMTMATH(1gmt)