Re: problem with using external functions

*To*: mathgroup at smc.vnet.net*Subject*: [mg91567] Re: problem with using external functions*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Thu, 28 Aug 2008 03:14:30 -0400 (EDT)*References*: <g93av9$k3e$1@smc.vnet.net>

Hi, you are right. And you should define your myintegrand[] in that way, i.e., myintegrand[x_?NumericQ,y_?NumericQ]:= .. Regards Jens Valery Yundin wrote: > Dear MathGroup, > > I've a problem with using external functions defined in MathLink app. > I guess the problem is in the evaluation order. I'm giving more > details below. > > This is the function template: > :Begin: > :Function: my_xfxM > :Pattern: xfxM[nset_Integer, x_Real, Q_] > :Arguments: {nset, x, Q} > :ArgumentTypes: {Integer, Real64, Real64} > :ReturnType: Manual > :End: > > The function body (the return value is list of doubles): > void my_xfxM(const int nset, const double x, const double Q) { > vector<double> result = LHAPDF::xfxM(nset, x, Q); > double* c_result = &(*result.begin()); > MLPutReal64List(stdlink, c_result, result.size()); > } > > I'm defining another function in Mathematica: > (it should multiply list of values returned by fucntion call by reversed > list of another function call and drop first 7 elements. > eg. if xfxM(1, x, 100.) returns {x1, ..., x14} the result should be: > Plus@@{x8*y14,x9*y13,...,x14*y8}) > myintegrand = > Function[{x, y}, > (Plus @@ (Drop[xfxM[1, x, 100.] Reverse[xfxM[1, y, 100.]], 7]))] > > Direct evaluation works well > myintegrand[0.5, 0.3] > > But smth like this does not work: > myintegrand[x, y] /. {x->0.5, y->0.3} > > And also when I try to integrate this function: > NIntegrate[myintegrand[x, y], {x, 0.001, 1}, {y, 0.001, 1}, > Method -> {"LocalAdaptive"}] > > The NIntegrate gives error message: > Drop::drop: Cannot drop positions 1 through 7 in xfxM[1,x,100.] \ > xfxM[100.,y,1]. >> > NIntegrate::inum: "Integrand (7+xfxM[1,x,100.]\xfxM[100.,y,1])/(14000\ > \x\y) is not numerical at {x,y} = {0.50048828125`,0.50048828125`}" > > How should I define my function to make this work? I think the problem is > that Mathematica tries to evaluate function body with formal parameters > (of "Symbol" type) not with just numerical values. > > -- > With best regards, Valery Yundin. >