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## Solving equations using using arrays

The attached contains an expression I wish to use in a solver to determine x-amount of constants (the Q's) from a system of an equal amount of equations and unknowns (the constants). The problem in mathcad arises when I'm using multiple (two) arrays within the solve block.

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Accepted Solutions

## Re: Solving equations using using arrays

As already suggested, get rid of the summation and the indexing.

13 REPLIES 13

## Re: Solving equations using using arrays

You will have to specify a value for n first.

You will also have to provide at least a sample for the vector u and the square matrix lamda.Q so we have soemthing to play with.

## Re: Solving equations using using arrays

Can it be that you are looking for something like the attached?

EDIT: Of course you can get the result much easier using the inverse:

## Re: Solving equations using using arrays

Something like that but I need to include summation over one of the indices.

"Funny" thing is I got it working a few minutes ago but the Mathcad shut down spontaneously and I can't get it working again. The error message is:"This variable is undefined"

## Re: Solving equations using using arrays

What you set up with your sum is exactly the multiplication of the matrix lamda.Q with the vector Q - thats the reason I posted my sheet in the last message.

The error messages in solve blocks are misleading - you will always get that "undefined variable", no matter what the real cause is. Right klick at the error message and chose "Trace Error" to get at least a message which may be a bit more useful.

## Re: Solving equations using using arrays

I've entered exactly what you you did in the attached but I still get that same error. It can be traced to the "i" index that supposedly has to be an integer.