Different results with ReplaceAll and direct substitution

*To*: mathgroup at smc.vnet.net*Subject*: [mg108936] Different results with ReplaceAll and direct substitution*From*: Alessio Giberti <giberti at fe.infn.it>*Date*: Wed, 7 Apr 2010 07:26:14 -0400 (EDT)

Hi all. A vector function of one variable, defined as follows, Y=expA[z].(Y0+Integrate[expA[-s].b[s],{s,0,z}]) give me different results if I use ReplaceAll instead of writing directly the value of z: Y /. z -> 0 Out[41]= {0.207031, 0.408203, 0.50293, 0.40625, 0.206543, 0., -0.00195313, 0.00195313, 0., 0.} expA[0].(Y0 + Integrate[expA[-s].b[s], {s, 0, 0}]) Out[42]= {0.206431, 0.408134, 0.503139, 0.405617, 0.206019, 0., 0., 0., 0., 0.} Where expA[z] is a matrix (10x10 in this case), Y0 is a vector of constants and b is a vector of functions. Since the last 5 components of Y0 are all zero, the first result cannot be correct! Why these 2 different results?