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# INTEGRATE(4RHEOLEF) - Linux manual page online | Special files

Integrate a function or an expression.

Chapter
rheolef-6.7
integrate(4rheolef) rheolef-6.7 integrate(4rheolef)

## 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 the field class. (iii) When the expression involves both symbolic trial- and test-functions see test(2), the result is a bilinear form, represented by the field class.

## SYNOPSYS

Float integrate (geo domain); Float integrate (geo domain, quadrature_option_type qopt); Value integrate (geo domain, Expression, quadrature_option_type qopt); field integrate (Expression); field integrate (Expression, quadrature_option_type qopt); field integrate (geo domain, Expression); field integrate (geo domain, Expression, quadrature_option_type qopt); form integrate (Expression); form integrate (Expression, form_option_type qopt); form integrate (geo domain, Expression); form integrate (geo domain, Expression, form_option_type 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_type qopt; qopt.set_order (3); Float int_f = integrate (omega, f, qopt); The last argument specifies the quadrature formulae (see quadrature_option_type(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 function f: 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 expression u*v can 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 is 2*k+1 where k is the polynomial degree of the Xh space associated to the test function v. When both a test u and trial v functions are suppied, let k1 and k2 be their polynomial degrees. Then the default quadrature is choosen to be exact at least for k1+k2+1 polynoms. When the integration is perfomed on a subdomain, this subdo‐ main 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.