Add core/biogeography.

Author: higham

core/private/biogeography.m

@@ -0,0 +1,17 @@
+function [A,properties] = biogeography(n) 
+%BIOGEOGRAPHY   Tridiagonal matrix with nonpositive eigenvalues.
+%   A = BIOGEOGRAPHY(N) is a singular N-by-N tridiagonal matrix
+%   with negative eigenvalues
+%   -2, -2*(n-2)/(n-1), ..., -4/(n-1), -2/(n-1), 0.
+%   This matrix can be written as
+%   -eye(n) + anymatrix('gallery/clement',n)/(n-1).
+
+%   Reference:
+%   B. Igelnik and D. Simon, The Eigenvalues of a Tridiagonal
+%   Matrix in Biogeography, Appl. Math. Comput. 218, 195-201, 2011.
+
+properties = {'tridiagonal', 'eigenvalues', 'sparse'};
+if nargin == 0, A = []; return, end
+
+c = (1:n-1)/(n-1);
+A = gallery('tridiag',c(n-1:-1:1),-ones(n,1),c);

core/private/edelman27.m

@@ -5,7 +5,7 @@
 %   >> format long g, det(A)
 %   ans =
 %              839466457497601
-%   yet the exact dterminant is 839466457497600.
+%   yet the exact determinant is 839466457497600.
 %   The matrix was found by Alan Edelman.
 %   Strange as it may seem, this behavior does not indicate anything is
 %   wrong with the det function and it is consistent with rounding error

readme.md

@@ -20,6 +20,7 @@ Currently, the built-in collection contains matrices organized into 7 groups:
 
 The following matrices have been added since v1.0.
 
+- core/biogeography
 - core/collatz
 - core/hess_sublu
 - core/milnes