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Substitutions


Hi
     Ive had this problem come up quite often and I was wondering if
     someone could help me. I have expressions that are quite complex
and
     what I would like to do is define a new non-dimensional parameter
that
     would have many of the variables of the expression clumped in it
and
     that would reduce the complexity of my expression. I have used /.
but
     Ive realized that unless what I want to replace is of the exact
     fractional form it wont substitute.
     This is my problem
http://mit.edu/shahriar/Public/1.bmp
     and say I want to rewrite this equation using new non-dimensional
parameters such
http://mit.edu/shahriar/Public/2.bmp
     Another example of this is I have an equation (http://mit.edu/
shahriar/Public/3.bmp ) and I want to replace Bx/=CE=BC0 with a new
variable say B_x Mathematica wont do it unless it is exactly like the
form Bx/=CE=BC0 so a rule like Bx/=CE=BC0 ->B_x is useless in dealing with =
this.
     If someone would help, i would be very grateful. Thanks



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