69 lines
1.8 KiB
C
69 lines
1.8 KiB
C
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#include <stdio.h>
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#include <math.h>
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#include <stdlib.h>
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typedef float(*function)(float);
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//(-2, -1.5) (-1.5, -1) (-1, -0.5) (-0.5, 0)
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float f(float x) {
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return 8*x*x*x*x + 32*x*x*x + 40*x*x + 16*x + 1;
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}
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float testf(float x){
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return 2;
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}
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float calcIntegralSquare(float xl, float xr, size_t n, function f) {
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float sum = 0;
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float h = (xr-xl)/n;
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for(size_t i=0; i<n; i++) {
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sum += f(xl);
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xl += h;
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}
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return sum*h;
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}
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float calcIntegralTrap(float xl, float xr, size_t n, function f) {
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float sum = 0;
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float h = (xr-xl)/n;
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for(float x=xl+h; x<xr-h; x+=h) {
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sum += 0.5*h*(f(x)+f(x+h));
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}
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return sum;
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}
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float calcIntegralSimpson(float xl, float xr, size_t n, function f) {
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float sum = 0;
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float h = (xr-xl)/n;
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for(float x=xl+h; x<xr-h; x+=h) {
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sum += h/6.0*(f(x) + 4.0*f(0.5*(x+x+h)) + f(x+h));
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}
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return sum;
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}
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float calcIntegralMonteCarlo(float xl, float xr, float fmax, size_t n, function f) {
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size_t in_d = 0;
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float width = fabs(xr-xl), height = fmax;
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for(size_t i=0; i<n; i++) {
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float x = ((float)rand()/(float)RAND_MAX) * width - fabs(xl);
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float y = (float)rand()/(float)RAND_MAX * height;
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if(y<f(x))
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in_d++;
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}
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return fabs( (float)in_d / n * width * height );
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}
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int main()
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{
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printf("calcIntegralSquare integral %f\n", calcIntegralSquare(0,2,1000,testf));
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printf("calcIntegralSquare = %f\n", calcIntegralSquare(-1.382683,-0.617316,1000,f));
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printf("calcIntegralTrap = %f\n", calcIntegralTrap(-1.382683,-0.617316,1000,f));
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printf("calcIntegralSimpson = %f\n", calcIntegralSimpson(-1.382683,-0.617316,1000,f));
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printf("calcIntegralMonteCarlo = %f\n", calcIntegralMonteCarlo(-1.382683,-0.617316,1,100000,f));
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return 0;
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}
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