[英]Trying to integrate an interpolated function with C GSL
I am new to the C language and I'm having some trouble with type declaration and pointers. 我是C语言的新手,我在类型声明和指针方面遇到了一些麻烦。
I'm trying to interpolate a dataset then integrate it, both numerical methods are done using the C GSL library. 我正在尝试插入数据集然后对其进行集成,两种数值方法都是使用C GSL库完成的。 The code is adapted from GSL's manual examples on monte carlo integration and 2d interpolation.
该代码改编自GSL关于蒙特卡罗积分和二维插值的手册示例。 Before using a dataset, I'm doing a test using a known and very simple 2D function.
在使用数据集之前,我正在使用已知且非常简单的2D函数进行测试。
The 2D interpolation part is working well, and I can obtain values from the interpolated function, interpFun
. 2D插值部分运行良好,我可以从插值函数
interpFun
获取值。
But I cannot use this interpolated function as input to the integration algorithm. 但是我不能使用这个插值函数作为积分算法的输入。
#include <stdio.h>
#include <stdlib.h>
#include <gsl/gsl_math.h>
#include <gsl/gsl_interp2d.h>
#include <gsl/gsl_spline2d.h>
#include <gsl/gsl_monte.h>
#include <gsl/gsl_monte_vegas.h>
int
main()
{
const gsl_interp2d_type *T = gsl_interp2d_bilinear;
const size_t N = 100; /* number of points to interpolate */
double xa[] = { 0.0, 1.0 }; /* define unit square */
double ya[] = { 0.0, 1.0 };
double xl[] = { 0., 0.};
double xu[] = { 1., 1.}, xp[] = {1.0, 0.0}, zz[] = {.2,.6};
const size_t nx = sizeof(xa) / sizeof(double); /* x grid points */
const size_t ny = sizeof(ya) / sizeof(double); /* y grid points */
double *za = malloc(nx * ny * sizeof(double));
double fun( double *x, size_t dim, void *params);
gsl_spline2d *spline = gsl_spline2d_alloc(T, nx, ny);
gsl_interp_accel *xacc = gsl_interp_accel_alloc();
gsl_interp_accel *yacc = gsl_interp_accel_alloc();
size_t i, j;
const gsl_rng_type *S;
gsl_rng *r;
double res, err;
struct fparams { gsl_spline2d *spline; gsl_interp_accel *xacc; gsl_interp_accel *yacc; };
/* set z grid values */
gsl_spline2d_set(spline, za, 0, 0, fun( xl, 2, 0) );
gsl_spline2d_set(spline, za, 0, 1, fun( xa, 2, 0) );
gsl_spline2d_set(spline, za, 1, 1, fun( xu, 2, 0) );
gsl_spline2d_set(spline, za, 1, 0, fun( xp, 2, 0) );
/* initialize interpolation */
gsl_spline2d_init(spline, xa, ya, za, nx, ny);
struct fparams params1 = { spline, xacc, yacc };
double interpFun( double *x, size_t dim, struct fparams p ) {
(void)(dim);
struct fparams *par = &p;
return gsl_spline2d_eval(par->spline, x[0], x[1], par->xacc, par->yacc);
};
gsl_monte_function G = { &interpFun, 2, ¶ms1 };
size_t calls = 500000;
gsl_rng_env_setup ();
S = gsl_rng_default;
r = gsl_rng_alloc (S);
{
gsl_monte_vegas_state *s = gsl_monte_vegas_alloc (2);
gsl_monte_vegas_integrate (&G, xl, xu, 2, 10000, r, s, &res, &err);
printf ("result = %.6f\n", res);
printf ("sigma = %.6f\n", err);
printf ("converging...\n");
do
{
gsl_monte_vegas_integrate (&G, xl, xu, 2, calls/5, r, s, &res, &err);
printf ("result = %.6f sigma = %.6f "
"chisq/dof = %.1f\n", res, err, gsl_monte_vegas_chisq (s));
}
while (fabs (gsl_monte_vegas_chisq(s)-1.0) > 0.5);
printf ("result = %.6f\n", res);
printf ("sigma = %.6f\n", err);
gsl_monte_vegas_free (s);
}
gsl_rng_free (r);
gsl_spline2d_free(spline);
gsl_interp_accel_free(xacc);
gsl_interp_accel_free(yacc);
free(za);
return 0;
}
double fun( double *x, size_t dim, void *p ) {
(void)(dim);
(void)(p);
return 3*x[0]+5*x[1];
}
This code returns the error message: 此代码返回错误消息:
inter_test.c: In function ‘main’:
inter_test.c:55:3: warning: initialization from incompatible pointer type [enabled by default]
gsl_monte_function G = { &interpFun, 2, ¶ms1 };
^
inter_test.c:55:3: warning: (near initialization for ‘G.f’) [enabled by default]
If I try integrating fun
instead of interpFun
, there is no error message, but both are the same type. 如果我尝试集成
fun
而不是interpFun
,则没有错误消息,但两者都是相同的类型。
The interpFun()
function as defined in your program has type double (*)(double *, size_t, struct fparams)
, but according to the GSL docs you need the type to be double (*)(double *, size_t, void *)
. 你的程序中定义的
interpFun()
函数有double (*)(double *, size_t, struct fparams)
,但根据GSL文档,你需要类型为double (*)(double *, size_t, void *)
。 Here is a fix: 这是一个修复:
double interpFun( double *x, size_t dim, void *p ) {
(void)(dim);
struct fparams *par = (struct fparams *) p;
return gsl_spline2d_eval(par->spline, x[0], x[1], par->xacc, par->yacc);
}
Additionally, C does not allow nested function definitions, though there is a GCC extension for this . 此外,C不允许嵌套函数定义,尽管有一个GCC扩展 。
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