Hi Bob,

not sure if this is what you want. First we take your matrices:

e = {{1}}; 
a = {{2, 2}, {2, 2}} ; b = {{3, 3, 3}, {3, 3, 3}, {3, 3, 3}}; 
c = {{4,4, 4, 4}, {4, 4, 4, 4}, {4, 4, 4, 4}, {4, 4, 4, 4}} ; 
d = {{5, 5, 5, 5, 5}, {5, 5, 5, 5, 5}, {5, 5, 5, 5, 5}, {5, 5, 5, 5, 5}, {5, 5,5, 5, 5}};

And then we do this:

list = {e, a, b, c, d}; matr = ConstantArray[0, {5, 5}]; For[i = 1, i <= 5, i++, matr[[i, i]] = list[[i]]]; 
ArrayFlatten[matr] // MatrixForm

which gives

Best wishes,

Marco

That is if you have not executed the first bit:

e = {{1}}; 
a = {{2, 2}, {2, 2}} ; b = {{3, 3, 3}, {3, 3, 3}, {3, 3, 3}}; 
c = {{4,4, 4, 4}, {4, 4, 4, 4}, {4, 4, 4, 4}, {4, 4, 4, 4}} ; 
d = {{5, 5, 5, 5, 5}, {5, 5, 5, 5, 5}, {5, 5, 5, 5, 5}, {5, 5, 5, 5, 5}, {5, 5,5, 5, 5}};

If you execute this and then

list = {e, a, b, c, d}; matr = ConstantArray[0, {5, 5}]; For[i = 1, i <= 5, i++, matr[[i, i]] = list[[i]]]; 
ArrayFlatten[matr] // MatrixForm

it will work.

Cheers,

Marco