Create a symmetric matrix in Mathematica

Bojan — Wed, 18 Nov 2009 19:03:20 +0000

Here is a quick way to create a symmetric matrix in Mathematica. The code below creates a generic 6×6 matrix (line 1), then mirrors the above-diagonal elements to their below-diagonal counterparts (substitution in lines 3-5).

am = Array[Subscript[a,##] &, {6,6}];
am = am /.
  Flatten[Table[
    Subscript[a,i,j] -> Subscript[a,j,i],
    {i,2,6}, {j,1,i-1}]]

Function call counting in Matlab

Bojan — Thu, 23 Mar 2006 13:38:15 +0000

Here’s a neat way to keep track of the cost, i.e. number of function calls in Matlab: rather than using a counter variable and increment it each time a function is called, use the internal Matlab counters, accessible through the FunctionTable struct array.

The loop below is necessary only to get the index of the desired function in the struct array (If you know a better way of looking up a function in FunctionTable, let me know!).

Replace the function name ftest if needed.

profile on

% your code comes here
% (cost is counted from "profile on" to "profile off")

p = profile('info');
for i = 1:size(p.FunctionTable,1)
    if strcmp(p.FunctionTable(i).FunctionName,'ftest')
        break
    end
end
cost = p.FunctionTable(i).NumCalls;
profile off

bojan.blog » Scientific Computing

Create a symmetric matrix in Mathematica

Function call counting in Matlab