Provided by: gmt-manpages_3.4.4-1_all bug


       grdmath - Reverse Polish Notation calculator for grd files


       grdmath  [  -F ] [ -Ixinc[m|c][/yinc[m|c]] -Rwest/east/south/north -V] operand [ operand ]
       OPERATOR [ operand ] OPERATOR ... = outgrdfile


       grdmath will perform operations like add, subtract, multiply, and divide on  one  or  more
       grd  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 grd file. When two grd files are on the stack, each
       element in file A is modified by the corresponding  element  in  file  B.   However,  some
       operators  only require one operand (see below). If no grdfiles are used in the expression
       then options -R, -I must be set (and optionally -F).

              If operand can be opened as a file it will be read as a grd file. If not a file, it
              is interpreted as a numerical constant or a special symbol (see below).

       outgrdfile is a 2-D grd file that will hold the final result.

              Choose among the following operators:
              Operator n_args Returns

              ABS 1 abs (A).
              ACOS 1 acos (A).
              ACOSH 1 acosh (A).
              ADD(+) 2 A + B.
              AND 2 NaN if A and B == NaN, B if A == NaN, else A.
              ASIN 1 asin (A).
              ASINH 1 asinh (A).
              ATAN 1 atan (A).
              ATAN2 2 atan2 (A, B).
              ATANH 1 atanh (A).
              BEI 1 bei (A).
              BER 1 ber (A).
              CDIST 2 Cartesian distance between grid nodes and stack x,y.
              CEIL 1 ceil (A) (smallest integer >= A).
              CHIDIST 2 Chi-squared-distribution P(chi2,nu), with chi2 = A and nu = B.
              COS 1 cos (A) (A in radians).
              COSD 1 cos (A) (A in degrees).
              COSH 1 cosh (A).
              CURV 1 Curvature of A (Laplacian).
              D2DX2 1 d^2(A)/dx^2 2nd derivative.
              D2DY2 1 d^2(A)/dy^2 2nd derivative.
              D2R 1 Converts Degrees to Radians.
              DDX 1 d(A)/dx 1st derivative.
              DDY 1 d(A)/dy 1st derivative.
              DILOG 1 Dilog (A).
              DIV(/) 2 A / B.
              DUP 1 Places duplicate of A on the stack.
              ERF 1 Error function of A.
              ERFC 1 Complementory Error function of A.
              ERFINV 1 Inverse error function of A.
              EQ 2 1 if A == B, else 0.
              EXCH 2 Exchanges A and B on the stack.
              EXP 1 exp (A).
              EXTREMA  1  Local  Extrema:  +2/-2 is max/min, +1/-1 is saddle with max/min in x, 0
              FDIST 4 F-dist Q(var1,var2,nu1,nu2), with var1 = A, var2 = B, nu1 = C, and nu2 = D.
              FLOOR 1 floor (A) (greatest integer <= A).
              FMOD 2 A % B (remainder).
              GDIST 2 Great distance (in degrees) between grid nodes and stack lon,lat.
              GE 2 1 if A >= B, else 0.
              GT 2 1 if A > B, else 0.
              HYPOT 2 hypot (A, B).
              I0 1 Modified Bessel function of A (1st kind, order 0).
              I1 1 Modified Bessel function of A (1st kind, order 1).
              IN 2 Modified Bessel function of A (1st kind, order B).
              INV 1 1 / A.
              ISNAN 1 1 if A == NaN, else 0.
              J0 1 Bessel function of A (1st kind, order 0).
              J1 1 Bessel function of A (1st kind, order 1).
              JN 2 Bessel function of A (1st kind, order B).
              K0 1 Modified Kelvin function of A (2nd kind, order 0).
              K1 1 Modified Bessel function of A (2nd kind, order 1).
              KN 2 Modified Bessel function of A (2nd kind, order B).
              KEI 1 kei (A).
              KER 1 ker (A).
              LE 2 1 if A <= B, else 0.
              LMSSCL 1 LMS scale estimate (LMS STD) of A.
              LOG 1 log (A) (natural log).
              LOG10 1 log10 (A).
              LOG1P 1 log (1+A) (accurate for small A).
              LOWER 1 The lowest (minimum) value of A.
              LT 2 1 if A < B, else 0.
              MAD 1 Median Absolute Deviation (L1 STD) of A.
              MAX 2 Maximum of A and B.
              MEAN 1 Mean value of A.
              MED 1 Median value of A.
              MIN 2 Minimum of A and B.
              MODE 1 Mode value (LMS) of A.
              MUL(x) 2 A * B.
              NAN 2 NaN if A == B, else A.
              NEG 1 -A.
              NRAND 2 Normal, random values with mean A and std. deviation B.
              OR 2 NaN if A or B == NaN, else A.
              PLM 3 Associated Legendre polynomial P(-1<A<+1) degree B order C.
              POP 1 Delete top element from the stack.
              POW(^) 2 A ^ B.
              R2 2 R2 = A^2 + B^2.
              R2D 1 Convert Radians to Degrees.
              RAND 2 Uniform random values between A and B.
              RINT 1 rint (A) (nearest integer).
              SIGN 1 sign (+1 or -1) of A.
              SIN 1 sin (A) (A in radians).
              SIND 1 sin (A) (A in degrees).
              SINH 1 sinh (A).
              SQRT 1 sqrt (A).
              STD 1 Standard deviation of A.
              STEP 1 Heaviside step function: H(A).
              STEPX 1 Heaviside step function in x: H(x-A).
              STEPY 1 Heaviside step function in y: H(y-A).
              SUB(-) 2 A - B.
              TAN 1 tan (A) (A in radians).
              TAND 1 tan (A) (A in degrees).
              TANH 1 tanh (A).
              TDIST 2 Student's t-distribution A(t,nu) = 1 - 2p, with t = A, and nu = B.'
              UPPER 1 The highest (maximum) value of A.
              XOR 2 B if A == NaN, else A.
              Y0 1 Bessel function of A (2nd kind, order 0).
              Y1 1 Bessel function of A (2nd kind, order 1).
              YLM 2 Re and Im normalized surface harmonics (degree A, order B).
              YN 2 Bessel function of A (2nd kind, order B).

              The following symbols have special meaning:

              PI 3.1415926...
              E  2.7182818...
              X  Grid with x-coordinates
              Y  Grid with y-coordinates


       -I     x_inc [and optionally y_inc] is the grid spacing. Append m to indicate minutes or c
              to indicate seconds.

       -R     west,  east, south, and north specify the Region of interest. To specify boundaries
              in degrees and minutes [and seconds], use the dd:mm[:ss] format. Append r if  lower
              left and upper right map coordinates are given instead of wesn.

       -F     Select pixel registration (used with -R, -I). [Default is grid registration].

       -V     Selects  verbose  mode,  which  will  send progress reports to stderr [Default runs


       The operator GDIST calculates spherical distances bewteen the  (lon,  lat)  point  on  the
       stack  and  all  node  positions in the grid. The grid domain and the (lon, lat) point are
       expected to be in degrees. The operator YLM  calculates  the  fully  normalized  spherical
       harmonics  for  degree L and order M for all positions in the grid, which is assumed to be
       in degrees.  YLM returns two grids, the Real (cosine) and Imaginary  (sine)  component  of
       the complex spherical harmonic. Use the POP operator (and EXCH) to get rid of one of them.
       The operator PLM calculates the associated Legendre polynomial of degree L  and  order  M,
       and  its argument is the cosine of the colatitude which must satisfy -1 <= x <= +1. Unlike
       YLM, PLM is not normalized.
       All the derivatives are  based  on  central  finite  differences,  with  natural  boundary


       To take log10 of the average of 2 files, use
               grdmath file1.grd file2.grd ADD 0.5 MUL LOG10 = file3.grd

       Given the file ages.grd, which holds seafloor ages in m.y., use the relation depth(in m) =
       2500 + 350 * sqrt (age) to estimate normal seafloor depths:
               grdmath ages.grd SQRT 350 MUL 2500 ADD = depths.grd

       To find the angle a (in degrees) of the largest principal stress from  the  stress  tensor
       given by the three files s_xx.grd s_yy.grd, and s_xy.grd from the relation tan (2*a) = 2 *
       s_xy / (s_xx - s_yy), try
               grdmath 2 s_xy.grd MUL s_xx.grd s_yy.grd SUB DIV ATAN2 2 DIV = direction.grd

       To calculate the fully normalized spherical harmonic of degree 8 and order 4 on a 1  by  1
       degree world map, using the real amplitude 0.4 and the imaginary amplitude 1.1, try
               grdmath -R0/360/-90/90 -I1 8 4 YML 1.1 MUL EXCH 0.4 MUL ADD = harm.grd

       To extract the locations of local maxima that exceed 100 mGal in the file faa.grd, try
               grdmath faa.grd DUP EXTREMA 2 EQ MUL DUP 100 GT NAN MUL = z.grd
               grd2xyz z.grd -S >


       Files  that  has  the same name as some operators, e.g., ADD, SIGN, =, etc. cannot be read
       and must not be present in the current directory. Piping of files are  not  allowed.   The
       stack  limit  is  hard-wired to 50.  All functions expecting a positive radius (e.g., log,
       kei, etc.) are passed the absolute value of their argument.


       Abramowitz, M., and I. A.  Stegun,  1964,  Handbook  of  Mathematical  Functions,  Applied
       Mathematics Series, vol. 55, Dover, New York.
       Press,  W. H., S. A. Teukolsky, W. T. Vetterling, B. P. Flannery, 1992, Numerical Recipes,
       2nd edition, Cambridge Univ., New York.


       gmt(1gmt), gmtmath(1gmt), grd2xyz(1gmt), grdedit(1gmt), grdinfo(1gmt), xyz2grd(1gmt)

                                            1 Jan 2004                                 GRDMATH(l)