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122 lines
3.6 KiB
Matlab
122 lines
3.6 KiB
Matlab
## Algorithm 3 from P. Maponi,
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## p. 283, doi:10.1016/j.laa.2006.07.007
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clc ## Clear the screen
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### Define the matrix to be inverted. This is example 8 from the paper
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### In the future this matrix needs to be read from the function call arguments
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#A=[1,1,-1; ...
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# 1,1,0; ...
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# -1,0,-1];
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#A0=diag(diag(A)); ## The diagonal part of A
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### The modified example that gives all singular updates at some point
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#A=[1,1,1; ...
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# 1,1,0; ...
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# -1,0,-1];
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#A0=diag(diag(A)); ## The diagonal part of A
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### A square uniform distributed random integer matrix with entries in [-1,1]
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#do
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# A=randi([-1,1],4,4);
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# A0=diag(diag(A)); ## The diagonal part of A
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#until (det(A)!=0 && det(A0)!=0) ## We need both matrices to be simultaniously non-singular
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## Define the matrix to be inverted. This is example 8 from the paper
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## In the future this matrix needs to be read from the function call arguments
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A=[1,0, 1,-1; ...
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0, 1, 1, 0; ...
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-1,0,-1, 0; ...
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1,1, 1, 1];
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A0=diag(diag(A)); ## The diagonal part of A
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### A square uniform distributed random float matrix with entries in (0,1)
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#do
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# A=rand(5);
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# A0=diag(diag(A)); ## The diagonal part of A
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#until (det(A)!=0 && det(A0)!=0) ## We need both matrices to be simultaniously non-singular
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Ar=A-A0; ## The remainder of A
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nCols=columns(Ar); ## The number of coluns of A (M in accompanying PDF)
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Id=eye(nCols);
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A0inv=eye(nCols);
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Ainv=zeros(nCols,nCols);
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ylk=zeros(nCols,nCols,nCols);
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p=zeros(nCols,1);
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breakdown=zeros(nCols,1);
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cutOff=1e-10
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A,A0
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printf("Determinant of A is: %d\n",det(A))
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printf("Determinant of A0 is: %d\n",det(A0))
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## Calculate the inverse of A0 and populate p-vector
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for i=1:nCols
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A0inv(i,i) = 1 / A0(i,i);
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p(i)=i;
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endfor
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## Calculate all the y0k in M^2 multiplications instead of M^3
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for k=1:nCols
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for i=1:nCols
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#printf("(i,k,1) = (%d,%d,1)\n",i,k);
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ylk(i,k,1) = A0inv(i,i) * Ar(i,k);
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endfor
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endfor
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## Calculate all the ylk from the y0k calculated previously
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for l=2:nCols
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## Calculate break-down conditions and put in a vector
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for j=l-1:nCols
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breakdown(j) = abs(1+ylk(p(j),p(j),l-1));
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#printf("|1 + ylk(%d,%d,%d)|\n", p(j), p(j), l-1);
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endfor
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[val, lbar] = max(breakdown); ## Find the index of the max value
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breakdown=zeros(nCols,1); ## Reset the entries to zero for next l-round
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## Swap p(l) and p(lbar)
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tmp=p(l-1);
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p(l-1)=p(lbar);
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p(lbar)=tmp;
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for k=l:nCols
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for i=1:nCols
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ylk(i,p(k),l) = ylk(i,p(k),l-1) - (ylk(p(l-1),p(k),l-1)) / (1+ylk(p(l-1),p(l-1),l-1)) * (ylk(i,p(l-1),l-1));
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#printf("ylk(%d,%d,%d) = ylk(%d,%d,%d) - (ylk(%d,%d,%d) / (1+ylk(%d,%d,%d) * (ylk(%d,%d,%d);\n", i,p(k),l,i,p(k),l-1,p(l-1),p(k),l-1,p(l-1),p(l-1),l-1,i,p(l-1),l-1);
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endfor
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endfor
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endfor
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## Construct A-inverse from A0-inverse and the ylk
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Ainv=A0inv;
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for l=1:nCols
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Ainv=(Id - ylk(:,p(l),l) * transpose(Id(:,p(l))) / (1 + ylk(p(l),p(l),l))) * Ainv;
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#printf("Ainv=(Id - ylk(:,%d,%d) * transpose(Id(:,%d)) / (1 + ylk(%d,%d,%d))) * Ainv\n",p(l),l,p(l),p(l),p(l),l);
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endfor
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## Test if the inverse found is really an inverse (does not work if values are floats)
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IdTest=A*Ainv;
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if (IdTest==eye(nCols))
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printf("\n");
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printf("Inverse of A^{-1} FOUND!\n");
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Ainv
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else
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printf("\n");
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printf("Inverse of A^{-1} NOT found yet.\nRunning another test...\n");
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for i=1:nCols
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for j=1:nCols
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if (abs(IdTest(i,j))<cutOff)
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IdTest(i,j)=0;
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elseif (abs(IdTest(i,j))-1<cutOff)
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IdTest(i,j)=1;
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endif
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endfor
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endfor
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if (IdTest==eye(nCols))
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printf("\n");
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printf("Inverse of A^{-1} FOUND!\n");
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Ainv
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else
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printf("\n");
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printf("Still not found. Giving up!\n");
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IdTest
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endif
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endif
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