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MathGroup Archive 2010

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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?


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