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VipulAcharya1-Visitor
1-Visitor
June 24, 2010
Question

Solving a system of equations

  • June 24, 2010
  • 29 replies
  • 14914 views

Hi:

I am completely new to MathCad and have a system of 6 equations that I need to solve. I have 6 variables and up to 12 "constants" that will change depending on my specific application. For example:

Variables are R1 to R6

"Constants" are various letters symbols.

How do I reduce the equations so that the 6 variables are solved in terms of the "constants"

I want to then take these expressions (variables in terms of constants) and put them in my spreadsheet for future use. Then I can change the constants in my spreadsheet and get the variable.

Can anyone help me?

Thanks.

29 replies

RichardJ19-Tanzanite
19-Tanzanite
June 24, 2010

It sounds like you are looking for a symbolic solution rather than a numeric one. Depending on the complexity of the equations there may be no such solution though, and even if there is it may be so large as to be effectively useless. Could you post a worksheet showing the 6 equations.

VipulAcharya1-VisitorAuthor
1-Visitor
June 24, 2010

Yes - I would like a symbolic solution.

I haven't even started entering them yet - I have them written on paper, but many of the symbols I want to use have subscript nomenclature such as

"Delta 1p", "Delta 2p", "Delta 3p.....Delta 6p" These are all upper case Deltas. They are all a function of P, L and L1 - L6. Nothing too complex, just multiplication, division, addition and exponents. Then I have,

"Delta 11", "Delta 21", "Delta 31.....Delta 61" these are lower case deltas. The are a function of R1, and all the Ls. same level of complexity. Then I have

"Delta 12", "Delta 22", "Delta 32.....Delta 62" lower case deltas, etc.... all the way to delta 66

So I have 36 small deltas and 6 big deltas. Then I have 7 Ls ( L, L1, L2, ...L6)

I have 6 equations:

delta11 + delta 21 + delta31...+delta61 = 0

delta 12 + delta 22 + ....+delta 62 = 0

etc

delta16 + delta26 + ....+ delta66 = 0

Then I want solve for R1 - R6 all interms of P and the 7 Ls.

I started entering the equations into the worksheet and it thinks the subscript p is a variable instead of a nomenclature thing.

I hope you can be patient with me

Thank you for your help.

RichardJ19-Tanzanite
19-Tanzanite
June 24, 2010
Nothing too complex, just multiplication, division, addition and exponents. Then I have,

That doesn't mean they will not be too complex. The exponents in particular could be a problem.

I started entering the equations into the worksheet and it thinks the subscript p is a variable instead of a nomenclature thing.

There are two types of subecript in Mathcad: a vector subscript, which you get with "[", and a literal subscript, which you get with ".". A vector subscript is an index into an array, and must therefore be a number or a variable. A literal subscript is just part of the variable name. You are obviously using vector subscripts, whereas you should be using literal subscripts.

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