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.TH psmall 1 "April 1993" "Scilab Group" "Scilab Function"
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psmall - spectral projection
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[Q,M]=psmall(A,thres,flag)
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: character string (\fV'c'\fR or \fV'd'\fR)
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Projection on eigen-subspace associated with eigenvalues
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with real part < \fVthres\fR (\fVflag='c'\fR) or with
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modulus < \fVthres\fR (\fVflag='d'\fR).
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The projection is defined by \fVQ*M\fR, \fVQ\fR is full column rank,
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\fVM\fR is full row rank and \fVM*Q=eye\fR.
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If \fVflag='c'\fR, the eigenvalues of \fVM*A*Q\fR = eigenvalues
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of \fVA\fR with real part < \fVthres\fR.
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If \fVflag='d'\fR, the eigenvalues of \fVM*A*Q\fR = eigenvalues
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of \fVA\fR with magnitude < \fVthres\fR.
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If \fVflag='c'\fR and if \fV[Q1,M1]\fR = full rank factorization (\fVfullrf\fR)
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of \fVeye()-Q*M\fR then eigenvalues of \fVM1*A*Q1\fR = eigenvalues
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of \fVA\fR with real part >= \fVthres\fR.
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If \fVflag='d'\fR and if \fV[Q1,M1]\fR = full rank factorization (\fVfullrf\fR)
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of \fVeye()-Q*M\fR then eigenvalues of \fVM1*A*Q1\fR = eigenvalues
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of \fVA\fR with magnitude >= \fVthres\fR.
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A=diag([1,2,3]);X=rand(A);A=inv(X)*A*X;
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[Q,M]=psmall(A,2.5,'d');
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[Q1,M1]=fullrf(eye()-Q*M);