X-Git-Url: http://gitweb.michael.orlitzky.com/?p=octave.git;a=blobdiff_plain;f=tridiagonal.m;fp=tridiagonal.m;h=ba99b6375c1bfa0bf9aa7dbce49c262ec30ba67f;hp=0000000000000000000000000000000000000000;hb=b49076a1d3f7f9d7830a4da5d9958636b9e5d903;hpb=b89ed48b92e5b38b7c8df70c12e4b8cc275628df

diff --git a/tridiagonal.m b/tridiagonal.m
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+++ b/tridiagonal.m
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+function A = tridiagonal(integerN, x, y, z)
+  %
+  % Construct the integerN x integerN (square) tridiagonal matrix
+  % diag(x,y,z).
+  %
+  % INPUT:
+  %
+  %   - ``integerN`` -- The dimensions of the resulting matrix.
+  %
+  %   - ``x`` -- The value on the subdiagonal.
+  %
+  %   - ``y`` -- The value on the diagonal.
+  %
+  %   - ``z`` -- The value on the superdiagonal.
+  %
+  if (integerN < 0)
+    A = NA;
+    return;
+  end
+
+  sub_diag = repmat(x, 1, integerN-1);
+  on_diag = repmat(y, 1, integerN);
+  super_diag = repmat(z, 1, integerN-1);
+  A = diag(on_diag) + diag(super_diag, 1) + diag(sub_diag, -1);
+end