True for letters of the alphabet
isletter
No equivalent
There is no equivalent function to Matlab isletter function in Scilab. However it can be replaced as follows. Using mtlb_isletter will give a prettier code.
tf = isletter(A)
// If A is a String matrix: tf = ((asciimat(A)>=65) & (asciimat(A)<=90)) | ((asciimat(A)>=97) & (asciimat(A)<=122)) // If A is not a String matrix: tf = zeros(A)