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POLabel used but not defined
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  1. POLabel used but not defined
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    copied!<p>I am trying to solve a linear systems of equations using LU decomposition followed by back substitution. However, in compiling it there is a problem, that states:</p> <pre><code>87:2: error: label ‘a’ used but not defined </code></pre> <p>Do you know what it means? Here is my program: </p> <pre><code>#include &lt;stdio.h&gt; #include &lt;math.h&gt; #include "nrutil.h" #include &lt;stdlib.h&gt; #define TINY 1.0e-20; void ludcmp(float **a, int n, int *indx, float *d) { int i,imax,j,k; float big,dum,sum,temp; float *vv; vv=vector(1,n); *d=1.0; for (i=1;i&lt;=n;i++) { big=0.0; for (j=1;j&lt;=n;j++) if ((temp=fabs(a[i][j])) &gt; big) big=temp; if (big == 0.0) nrerror("Singular matrix in routine ludcmp"); vv[i]=1.0/big; } for (j=1;j&lt;=n;j++) { for (i=1;i&lt;j;i++) { sum=a[i][j]; for (k=1;k&lt;i;k++) sum -= a[i][k]*a[k][j]; a[i][j]=sum; } big=0.0; for (i=j;i&lt;=n;i++) { sum=a[i][j]; for (k=1;k&lt;j;k++) sum -= a[i][k]*a[k][j]; a[i][j]=sum; if ( (dum=vv[i]*fabs(sum)) &gt;= big) { big=dum; imax=i; } } if (j != imax) { for (k=1;k&lt;=n;k++) { dum=a[imax][k]; a[imax][k]=a[j][k]; a[j][k]=dum; } *d = -(*d); vv[imax]=vv[j]; } indx[j]=imax; if (a[j][j] == 0.0) a[j][j]=TINY; if (j != n) { dum=1.0/(a[j][j]); for (i=j+1;i&lt;=n;i++) a[i][j] *= dum; } } free_vector(vv,1,n); } #undef TINY void lubksb(float **a, int n, int *indx, float b[]) { int i,ii=0,ip,j; float sum; for (i=1;i&lt;=n;i++) { ip=indx[i]; sum=b[ip]; b[ip]=b[i]; if (ii) for (j=ii;j&lt;=i-1;j++) sum -= a[i][j]*b[j]; else if (sum) ii=i; b[i]=sum; } for (i=n;i&gt;=1;i--) { sum=b[i]; for (j=i+1;j&lt;=n;j++) sum -= a[i][j]*b[j]; b[i]=sum/a[i][i]; } } int main(){ float a[3][3], c[3][3], b[3], d; int indx[3], i, j; a[1][1]=1.00; a[1][2]=0.80; a[1][3]=0.64; a[2][1]=1.00; a[2][2]=0.90; a[2][3]=0.81; a[3][1]=1.00; a[3][2]=1.10; a[3][3]=1.11; b[0]=erf(0.80); b[1]=erf(0.90); b[2]=erf(1.10); ludcmp(&amp;&amp;a, 3, indx, &amp;d); lubksb(&amp;&amp;a, 3, indx, b); for (i=0; i&lt;=3; i++) printf("%f", b[i]); return 0; } </code></pre>
 

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