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.

Sample Solution

#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
    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; 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
cs190c/lab2.txt · Last modified: 2008/04/18 11:38 (external edit)
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