data: apply(matrix, makelist(makelist(random(100), 20), 20))$
find_value(a, x) := block(
[p, q],
[p, q]: matrix_size(a),
catch(
for i thru p do
for j thru q do
if a[i, j] = x then throw([i, j]),
'not\ found
)
)$
find_value(data, 100);
not found