Re: Substitutions

*To*: mathgroup at smc.vnet.net*Subject*: [mg77896] Re: Substitutions*From*: "Shahriar Khushrushahi" <shahriar at mit.edu>*Date*: Tue, 19 Jun 2007 06:40:13 -0400 (EDT)*References*: <1181833391.078257.209380@x35g2000prf.googlegroups.com>

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/ì0 with a > new variable say B_x Mathematica wont do it unless it is exactly like the > form Bx/ì0 so a rule like Bx/ì0 ->B_x is useless in dealing with this. If someone would help, i would be very grateful. Thanks > >