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    copied!<p>I finally found it. I just need to implement the following code from matlab source code to c++ . "the_mandrill" were right, I need to add the normalizing constant into the coefficient:</p> <pre><code>kern = exp(-j*w*(0:length(b)-1)); b = real(b*(kern*den(:))/(kern*b(:))); </code></pre> <p><strong>EDIT:</strong> and here is the final edition, which the whole code will return numbers exactly equal to MATLAB : </p> <pre><code>double *ComputeNumCoeffs(int FilterOrder,double Lcutoff, double Ucutoff, double *DenC) { double *TCoeffs; double *NumCoeffs; std::complex&lt;double&gt; *NormalizedKernel; double Numbers[11]={0,1,2,3,4,5,6,7,8,9,10}; int i; NumCoeffs = (double *)calloc( 2*FilterOrder+1, sizeof(double) ); if( NumCoeffs == NULL ) return( NULL ); NormalizedKernel = (std::complex&lt;double&gt; *)calloc( 2*FilterOrder+1, sizeof(std::complex&lt;double&gt;) ); if( NormalizedKernel == NULL ) return( NULL ); TCoeffs = ComputeHP(FilterOrder); if( TCoeffs == NULL ) return( NULL ); for( i = 0; i &lt; FilterOrder; ++i) { NumCoeffs[2*i] = TCoeffs[i]; NumCoeffs[2*i+1] = 0.0; } NumCoeffs[2*FilterOrder] = TCoeffs[FilterOrder]; double cp[2]; double Bw, Wn; cp[0] = 2*2.0*tan(PI * Lcutoff/ 2.0); cp[1] = 2*2.0*tan(PI * Ucutoff / 2.0); Bw = cp[1] - cp[0]; //center frequency Wn = sqrt(cp[0]*cp[1]); Wn = 2*atan2(Wn,4); double kern; const std::complex&lt;double&gt; result = std::complex&lt;double&gt;(-1,0); for(int k = 0; k&lt;11; k++) { NormalizedKernel[k] = std::exp(-sqrt(result)*Wn*Numbers[k]); } double b=0; double den=0; for(int d = 0; d&lt;11; d++) { b+=real(NormalizedKernel[d]*NumCoeffs[d]); den+=real(NormalizedKernel[d]*DenC[d]); } for(int c = 0; c&lt;11; c++) { NumCoeffs[c]=(NumCoeffs[c]*den)/b; } free(TCoeffs); return NumCoeffs; } </code></pre>
 

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