Invert Matrix

From: Julia Campa Romero <Julia.Campa_at_ciemat.es>
Date: Wed, 5 Aug 2009 13:01:02 +0200

Hi,

I want to invert a 39x39 symetric matrix. But I have some difficulties. First, I fill the upper diagonal elements and then I complete it. The programa to fill the Matrix is:

---

   TMatrixD h(39,39);
   //CON are the values of the elements
   for (Int_t i=0;i<39;i++){

     for (Int_t j=i;j<39;j++){
     h[i][j]=CON[i][j];

 }   

   //completed the low diagonal elements    for (Int_t j=0;j<i;j++){
     h[i][j]=CON[j][i];     

    }    

   }

---

--Then to check whether the matrix is singular before attempting to
invert it I write:

---

       TDecompLU lu(h);
       TMatrixD p;
       if (!lu.Decompose()) {
       cout << "Decomposition failed, matrix singular ?" << endl;
      } else {
      lu.Invert(p);
       }

---

 And it gives me the following error:

 >>Error in <TDecompLU::Invert(TMatrixD &>: Input matrix has wrong shape

--Then when I made

  >TMatrixD hi=h.Invert();
It is gives me:
 >>Error in <TDecompLU::InvertLU>: matrix is singular, 1 diag elements < tolerance of 2.2204e-16

Could you explain me what it is happening?

Julia Campa

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Received on Wed Aug 05 2009 - 13:01:11 CEST