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st: RE: Parse (translate equalities into linear transformation matrix)

From   "Nick Cox" <>
To   <>
Subject   st: RE: Parse (translate equalities into linear transformation matrix)
Date   Fri, 2 Apr 2004 14:58:02 +0100

Two very broad suggestions: 

Why not turn the problem so that the user must input this 

Can you get -test- to do the work for you? 


Jun Xu
> Thanks to Nick's comments on syntax anything last time and I 
> used several 
> gettoken and equations get parsed. Now, I try to incorporate more 
> comprehensive problems. A reminder of my problem and to make 
> my problem more 
> generic, I have d1, d2, d3...(k known number of functions 
> derived from 
> estimated of last estimation), and I like to test if the 
> linear combination 
> of is equal to somthing, something like:
> let's assume there is d1-d5
> mytest 2*d1+(3+5)*d2/2+d5*_pi=0
> I can successfully parse each element before or after + or 
> negative sign, 
> but I couldn't figure out how to parse 2*d1, 3*d2/2, d5*_pi 
> into matrix. It 
> seems to me there are too many ways of writing such 
> expressions, thereby 
> hard to parse. The end product that I what is two matrices:
> The transformation matrix: [2, (3+5)/2, 0, 0, _pi]
> The d matrix: [d1, d2, d3, d4, d5]'
> Well, I can easily get d matrix because I can use some info in last 
> estimation to derive them, but the key issue here is to grab 
> numbers or 
> numeric expressions in those equalities, peel off d1, 
> d2,...d5, and turn the 
> rest part into a transformation matrix. Any suggestions? Thanks a lot.

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