51 lines
1.1 KiB
C
51 lines
1.1 KiB
C
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#define NRANSI
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#include "nrutil.h"
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void simpr(float y[], float dydx[], float dfdx[], float **dfdy, int n,
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float xs, float htot, int nstep, float yout[],
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void (*derivs)(float, float [], float []))
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{
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void lubksb(float **a, int n, int *indx, float b[]);
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void ludcmp(float **a, int n, int *indx, float *d);
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int i,j,nn,*indx;
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float d,h,x,**a,*del,*ytemp;
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indx=ivector(1,n);
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a=matrix(1,n,1,n);
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del=vector(1,n);
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ytemp=vector(1,n);
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h=htot/nstep;
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for (i=1;i<=n;i++) {
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for (j=1;j<=n;j++) a[i][j] = -h*dfdy[i][j];
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++a[i][i];
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}
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ludcmp(a,n,indx,&d);
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for (i=1;i<=n;i++)
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yout[i]=h*(dydx[i]+h*dfdx[i]);
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lubksb(a,n,indx,yout);
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for (i=1;i<=n;i++)
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ytemp[i]=y[i]+(del[i]=yout[i]);
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x=xs+h;
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(*derivs)(x,ytemp,yout);
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for (nn=2;nn<=nstep;nn++) {
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for (i=1;i<=n;i++)
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yout[i]=h*yout[i]-del[i];
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lubksb(a,n,indx,yout);
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for (i=1;i<=n;i++)
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ytemp[i] += (del[i] += 2.0*yout[i]);
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x += h;
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(*derivs)(x,ytemp,yout);
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}
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for (i=1;i<=n;i++)
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yout[i]=h*yout[i]-del[i];
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lubksb(a,n,indx,yout);
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for (i=1;i<=n;i++)
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yout[i] += ytemp[i];
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free_vector(ytemp,1,n);
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free_vector(del,1,n);
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free_matrix(a,1,n,1,n);
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free_ivector(indx,1,n);
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}
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#undef NRANSI
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