Help - Simple Mathcad issues in solving a given problem

[rctoliveira]

I am particularly new to Mathcad, and I was assigned a couple of problems in a Thermodynamics course I am taking. I would be most glad if somebody could please help me with a few issues I am having. They seem pretty simple and they must, in fact, be pretty easy to fix. I just couldn't really do it in spite of much effort, I'm guessing because of the little I have with Mathcad.

There are two (very short) files, both with problems:

12.6

In this problem, the function "minimize" won't run, stating that "the variable is undefined".

12.20

The function "find" won't run, also stating that "the variable is undefined.

So, it isn't much, but I could really use a hand here.

Thanks

[AlanStevens · Accepted solution]

See if the attached helps with 12.6.

In 12.20 you have confused x's that have true subscripts with x's that have cosmetic subscripts.

Alan

[rctoliveira]

Thank you so much! This was really helpful. Now back to work

[lturek]

And as for 12.20: replace the sum by x.1+x.2+x.3=1 does the job.

You variables x1 to x3 are using the literal index and You can't cycle through this literal index using a range or sum symbol.

As an alternative You could define x1-x3 as vector components by using the vector index x[1, etc. Then Your sum should work as expected.

[rctoliveira]

Thanks a lot, Leopold!