Provided by: librheolef-dev_7.0-3_amd64

**NAME**

integrate- integrate a function or an expression

**DESCRIPTION**

Integrate an expression over a domain by using a quadrature formulae. There are three main usages of the integrate function, depending upon the type of the expression. (i) When the expression is a numerical one, it leads to a numerical value. (ii) When the expression involves a symbolic test-function see test(2), the result is a linear form, represented by thefieldclass. (iii) When the expression involves both symbolic trial- and test-functions see test(2), the result is a bilinear form, represented by thefieldclass.

**SYNOPSIS**

Float integrate (geo domain); Float integrate (geo domain, quadrature_option qopt); Value integrate (geo domain, Expression, quadrature_option qopt); field integrate (Expression); field integrate (Expression, quadrature_option qopt); field integrate (geo domain, Expression); field integrate (geo domain, Expression, quadrature_option qopt); form integrate (Expression); form integrate (Expression, integrate_option qopt); form integrate (geo domain, Expression); form integrate (geo domain, Expression, integrate_option qopt);

**EXAMPLE**

For computing the measure of a domain: Float meas_omega = integrate (omega); For computing the integral of a function: Float f (const point& x); ... quadrature_option qopt; qopt.set_order (3); Float int_f = integrate (omega, f, qopt); The last argument specifies the quadrature formulae (see quadrature_option(2)) used for the computation of the integral. The function can be replaced by any field-valued expression (see field(2)). For computing a right-hand-side of a variational formulation with the previous functionf: space Xh (omega, "P1"); test v (Xh); field lh = integrate (f*v); For computing a bilinear form: trial u (Xh); test v (Xh); form m = integrate (u*v); The expressionu*vcan be replaced by any bilinear expression (see field(2)).

**DEFAULT** **ARGUMENTS**

In the case of a linear or bilinear form, the domain is optional: by default it is the full domain definition of the test function. Also, the quadrature formulae is optional: by default, its order is2*k+1wherekis the polynomial degree of theXhspace associated to the test functionv. When both a testuand trialvfunctions are supplied, let k1 and k2 be their polynomial degrees. Then the default quadrature is chosen to be exact at least for k1+k2+1 polynoms. When the integration is performed on a subdomain, this subdomain simply replace the first argument and a domain name could also be used: field l2h = integrate (omega["boundary"], f*v); field l3h = integrate ("boundary", f*v); For convenience, only the domain name can be supplied.

**SEE** **ALSO**

test(2), test(2), quadrature_option(2), field(2), field(2)

**COPYRIGHT**

Copyright (C) 2000-2018 Pierre Saramito <Pierre.Saramito@imag.fr> GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.