Question for SunnyCoder

Posted on 2004-04-24
Last Modified: 2010-08-05
Hey man. I wanted to write a program to process simple algebra problems..


3x + 15 = 11 - x
4x = -4
x = -1

how would you suggest going about this? I dont plan to write it in C, I was acctually going to write it in Visual Basic, but you are good with math, so I was curious how you would suggest doing it. So far I've created a type structure array to store all the monomials, but how do you suggest processing it, I'm stumpted. If you want to throw out some C code, I can port it to VB.

Question by:BrianGEFF719
LVL 84

Expert Comment

ID: 10910362
Will the problems be single variable linear equations like your example?

Expert Comment

ID: 10910474
Can we lowly creatures also participate in this question or you want only sunny's suggestion???
LVL 19

Author Comment

ID: 10914018
Everyone feel free to comment.

Right now I am going to focus on Single Variables.
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LVL 84

Expert Comment

ID: 10914618
If your problems will all be single variable linear equations you could just change = to -
evaluate at two x values, then extrapolate to where the expression equals 0
LVL 84

Expert Comment

ID: 10914637
(3x + 15) - (11 - x)
(3*0 + 15) - (11 - 0) = 4
(3*1 + 15) - (11 - 1) = 8
x = 4/(4-8) = -1
LVL 10

Expert Comment

ID: 10915044
To make it simple (e.g. without going to RPN resolution etc...) you have to get 4 variables
v1 is the number of x on left side
v2 is the number on left side (no x)
v3 is the number of x on right side
v4 is the number on right side (no x)

    e.g.  for 3x + 15 = 11 - x

    v1 = 3
    v2 = 15
    v3 = -1
    v4 = 11

The you calculate
     vx = v1 - v3
     vn = v4 - v2

And you have your result R = vn / vx

   vx = v1 - v3 = 4
   vn = -4
   R = 4 / -4 = -1

How to proceed programmatically (automat)
1 -   initialize all v1,v2,v3,v4 to 0.
2 -   parse the equation left side for v1, v2
3 -   set default sign is "+"
4 -   you get a sign : set sign to + or -
5 -   you get a number : put the number in N
6 -   number is followed by x : do v1 = v1 + N
7 -   number is not followed by x : do v2 = v2 + N
8 -   repeat from 3 etc...

Do the same right side, the vars being v3,v4
Once you get all v1...v4, calculate R as above.
LVL 10

Accepted Solution

Mercantilum earned 500 total points
ID: 10915054
of course of steps 5 and 6, N is signed by 'sign' (ie  N = N * sign ), sign being 1 if "+", -1 if "-"

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