Why does this vector not compute?

[gwestbrook]

Starting to feel a bit moronic here.

I've included a short worksheet illustrating my problem.  I'm trying to graduate from simple calculation to using vectors.  As you will see, I have an equation for M for which I can calculate a value easily enough.  Units work out OK too.

When I attempt to make a vector (in my world, this lambda equates to a wavelength but that's irrelevant to the problem), I get an error complaining of the units.

Not really sure if that's really the issue here; can anybody else shed some light?

[LucMeekes · Accepted solution]

You've put a multiplication between M and (lambda, 300*K), dissecting the function name from its argument list. Remove that and it should work fine.

Well not completely,  the funny error message is gone, but you get a single result for an input vector.

In order to get a vector of results, you need to vectorize the definition (the right-hand-side of the definition of the function M.

To do that, select it and press [CTRL -], it will show an arrow above. And the result of the last evaluation will be a vector.

Succes!
Luc

[StuartBruff]

In addition to the extra character between the M and the opening parenthesis,  you will need to use the vectorize operator (ctl-minus) to get a result for each lambda.  Otherwise Mathcad will interpret the  lambda multiplication in the  (power to the fifth and the exponential) as a vector dot product.

Stuart

[gwestbrook]

Thanks!

Based on the recommendation of someone on this forum, I've ordered "Essential MathCAD for Engineering, Science, and Math".  That should help me get better at this.

[MikeArmstrong]

I would highly recommend using this forum and the material passed by the members. Good luck.