struct2mat(S)

[X,n]= STRUCT2MAT(S) converts a structre S into a numeric matrix X. The
contents of each *numeric* field of S (either a vector or a matrix) will
form 1 column of X. Fieldnames are returned in cell array 'n'. If the
fields of S aren't of the same length, the columns of X will be padded
with NaN.
Example:
s= struct('a',['string of letters'],'b',[1 2; 3 4],'c',[1 2 3 4 5 6 7 8 9])
[x,n]= struct2mat(s)