Lab 2 Problem

Matrix multiplication using arrays.

• Read in number n which indicates the dimensions of the matrix.
• Create the matrix array with the zeros function, reading in n^2 numbers from file matrixA.txt.
• After reading in the matrix A, print out A.
• Next, read in n^2 numbers from file matrixB.txt.
• Next, print out matrix B.
• Note: solution below reads row by row and reads files simultaneously
• Then, use matrix multiplication to calculate A*B, and print out the result.
• Matrix multiplication reference.

#Lab 2, Lab problem 1 
#Course solution
 
def main():
    from numpy import zeros
    import string
 
    # Comments:
    # asking the user to input n is not a good idea in general; 
    # n can be determined from the first file line and file reading continues until no more input; or the 
    # first line of the file can contain n 
    # in lab assignments you can assume that the input data is "nice"
 
    n = input("Input the dimension of the matrices: ")
    n = int(n)
 
    fileA = open("matrixA.txt")  # open files as in bird.py
    fileB = open("matrixB.txt")
 
    matrixA = zeros((n,n))  # initialize all three arrays with zeros
    matrixB = zeros((n,n))
    result = zeros((n,n))
 
    # there exist a number of correct ways to read the two matrices; the one belows is
    # similar to the bird example from class
    for i in range(n):
            lineA = fileA.readline()    # use of readline and split operations
            lineB = fileB.readline()    # as in bird.py; here split is on space                                  
            rowA = string.split(lineA, " ") 
            rowB = string.split(lineB, " ")
 
            for j in range(n):                  # convert elements in the strings to integers 
                matrixA[i][j] = int(rowA[j])    # assign to individual array entries
                matrixB[i][j] = int(rowB[j])
 
    print "A: "
    print matrixA
    print "B: "
    print matrixB
 
    for i in range(n):      # double loop to generate all n^2 entries 
        for j in range(n):  # one loop to compute each entry
            for k in range(n):
                result[i][j] += matrixA[i][k] * matrixB[k][j]
 
    print "A*B: "
    print result
 
main()