使用C函数在其他RCPP包

问题描述

我想打电话从数值积分包在C A C ++程序函数执行多维整合。

I'm trying to call a C routine from the cubature package in a c++ function to perform multidimensional integration.

我试图重现基本科研的例子是

The basic R example I'm trying to reproduce is

library(cubature)
integrand <- function(x) sin(x)
adaptIntegrate(integrand, 0, pi)

我可以称之为从这个RCPP R函数如下 href=\"http://gallery.rcpp.org/articles/r-function-from-c++/\">这个配方，但将是从C / C ++来R.它似乎更为明智来直接调用C函数从C ++来回切换的性能损失。

I could just call this R function from Rcpp following this recipe from the gallery, but there would be some performance penalty in switching back and forth from c/c++ to R. It seems more sensible to directly call the C function from C++.

C例程 adapt_integrate 是数值积分导出的

 // R_RegisterCCallable("cubature", "adapt_integrate", (DL_FUNC) adapt_integrate);

我不知道如何把它从C ++调用然而，。这里是我的蹩脚的尝试，

I don't understand how to call it from c++, however. Here's my lame attempt,

sourceCpp(code = '
#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
double integrand(double x){
 return(sin(x));
}

// [[Rcpp::depends(cubature)]]
// [[Rcpp::export]]
Rcpp::List integratecpp(double llim, double ulim)
{
  Rcpp::Function p_cubature = R_GetCCallable("cubature", "adapt_integrate");

  Rcpp::List result = p_cubature(integrand, llim, ulim);
  return(result);
}
'
)

integratecpp(0, pi)

这编译失败;显然，我做的事情很无聊，并丢失了一些重要的措施来 R_GetCCallable 的输出转换成 RCPP ::功能（或者直接打电话吗？）。我读过一些相关的帖子处理函数指针，但还没有看到使用外部C函数的例子。

This fails to compile; clearly I'm doing something very silly and missing some important steps to convert the output of R_GetCCallable into an Rcpp::Function (or call it directly?). I've read several related posts dealing with function pointers, but haven't seen an example using an external C function.

推荐答案

不幸的是数值积分不出货的头在安装/包括，所以你不得不借，从他们的，做这样的事情在你的code：

Unfortunately cubature does not ship the headers in inst/include, so you have to borrow that from them and do something like this in your code:

typedef void (*integrand) (unsigned ndim, const double *x, void *,
           unsigned fdim, double *fval);

int adapt_integrate(
    unsigned fdim, integrand f, void *fdata,
    unsigned dim, const double *xmin, const double *xmax,
    unsigned maxEval, double reqAbsError, double reqRelError,
    double *val, double *err)
{
    typedef int (*Fun)(unsigned,integrand,void*,unsigned,
        const double*,const double*, unsigned, double, double, double*, double*) ;
    Fun fun = (Fun) R_GetCCallable( "cubature", "adapt_integrate" ) ;
    return fun(fdim,f,fdata,dim,xmin,xmax,maxEval,reqAbsError, reqRelError,val,err);
}

这可能是与数值积分的维护者，在他船声明安装/包括来negociate一个好主意这样你只需要使用 LinkingTo 。

It might be a good idea to negociate with the maintainer of cubature that he ships declarations in inst/include so that you'd only have to use LinkingTo.

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