This program gives me the message following it: ================Program========== import numpy as np from numpy import matrix import math def sinD(D): # given in degrees, convert to radians return math.sin(math.radians(D)) def cosD(D): return math.cos(math.radians(D)) r = math.sqrt(2*2+5*5) print r m1 = matrix([[2], [5]]) print "m1: ", m1 theta = 5.0 # degrees #CW 2x2 clockwise matrix rotCW = matrix([ [cosD(theta), sinD(theta)], [-sinD(theta), cosD(theta)] ]) print rotCW m2 = rotCW*m1 print "m2: ", m2 print "aaaaaaaa: ", type(m1), type(m2) m1=np.array(m1) m2=np.array(m2) print "zzzzzzzz: ", type(m1), type(m2) print"dot, ..." dotres = np.dot(m1,m2) print "dotres", dotres ==============end========== ==========Output msgs======== 5.38516480713 m1: [[2] [5]] [[ 0.9961947 0.08715574] [-0.08715574 0.9961947 ]] m2: [[ 2.42816811] [ 4.806662 ]] aaaaaaaa: <class 'numpy.core.defmatrix.matrix'> <class 'numpy.core.defmatrix.matrix'> zzzzzzzz: <type 'numpy.ndarray'> <type 'numpy.ndarray'> dot, ... Traceback (most recent call last): File "C:/Sponsor_Meteors/Sentinel_Development/Development_Sentuser+Utilities/Playground/junk.py", line 30, in <module> dotres = np.dot(m1,m2) ValueError: objects are not aligned ================end msgs=========== Why the msg? The types look alike and each array/matrix contains two elements.. -- Wayne Watson (Watson Adventures, Prop., Nevada City, CA) (121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time) Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet "... humans'innate skills with numbers isn't much better than that of rats and dolphins." -- Stanislas Dehaene, neurosurgeon Web Page: <www.speckledwithstars.net/>