Solving for values in a table

[MH_10178519]

Would love help with this.  I've defined my function, inserted a table of values, and am expecting results in a vector format. 

HELP!!

[LucMeekes]

Please attach the Prime worksheet, not just/only a picture.

Some upfront advice:

1. Make sure that k is defined.

2. Vectorize the expression at the right-hand side of the definition.

3. DON'T evaluate a definition. That is: do NOT put an '=' at the end of a definition. It may work in many cases, but in ever so many cases it leads to problems. Use a separate region to evaluate your expression.

Success!
Luc

[Werner_E]

You have to delete the equal sign after the function definition and evaluate the function in a separate region.

Furthermore I guess you will have to vectorize the function call as you will get wrong results otherwise.

I second what Luc already said - attach the worksheet!

EDIT: Ahh, I see that in the meanwhile Luc has edited his reply and suggests quite the same 😉

Another option would be that you don't define a function but a simple variable eta:=...
In this case you would have to use vectorization as well but you could use inline evaluation (the = after the definition). But for some reason inline evaluations have proven to be instable in some situations and so I suggest not using it.

BTW, inline evaluation never works when defining a function.

[MH_10178519]

File attached....

I am really new at this so I appreciate the patience...

When you say "vectorize" the function, how is that accomplished?  

[MH_10178519]

Whoops, sorry, I was working on a different computer and the file did not save.  I'll upload revised shortly.

[MH_10178519]

Updated worksheet attached.  Thanks!

[Werner_E]

vectorizing is the operator which shows as an arrow over the expression:

You may note that you can define the function above the table with values. They need not to be defined when you define your function.

So I would suggest to either define a function beforehand and the call it vectorized and assign the result to a variable or simply assign the definition (which is less preferable in my opinion).

[MH_10178519 · Accepted solution]

Ahhh, thanks a ton!  This worked!  Next is to figure out how to plot!  

Thanks a bunch.

M

[Werner_E]

Have edited my reply and attached the work sheet

[LucMeekes]

How to plot...

Assuming you'd want to plot the eta results, you'll have to decide what you want to plot it against:

r_c?

or r_x?

or all three?

success!

Luc

[StuartBruff]

---

@Werner_E wrote:

vectorizing is the operator which shows as an arrow over the expression:

You may note that you can define the function above the table with values. They need not to be defined when you define your function.

So I would suggest to either define a function beforehand and the call it vectorized and assign the result to a variable or simply assign the definition (which is less preferable in my opinion).

---

I'd have been tempted to put the vectorize operator inside the function.

Stuart

[Fred_Kohlhepp]

Add two statements:

You've defined  a function, which is what Prime is saying with the statement 

So you can define a variable (N) to evaluate each occurrance of the r_c, r_x, and r_k (which is what the "vectorization" (the arrow above the function) does, and then you can see each N.  (Which is what Luc and Werner were saying.)

[MH_10178519]

I think i understand now.  if the variable is in a vector format, then the resulting equation or function must also be in a vector format...

[LucMeekes]

"if the variable is in a vector format, then the resulting equation or function must also be in a vector format"

Often, but not necessarily. You can write a function

that accepts two vectors

and results in a single number,

or in a matrix

(Note that

)

But if you use vectors to hold sets of values that you want to operate on as sets, like you do here, you mostly need to vectorise the expression.

and beware. The function:

supplied with the same variables, results in respectively:

(complaint that the array dimensions do not match)

(vectorisation results in no diffent operation for addition of two vectors)

Success!
Luc

[StuartBruff]

---

@MH_10178519 wrote:

I think i understand now.  if the variable is in a vector format, then the resulting equation or function must also be in a vector format...

---

Just to amplify the point others have made, it's the nature of the vector operations that determine whether you need to vectorize a result.  Mathcad operators and functions generally have a vector/matrix interpretation if there is one, otherwise they will either raise an error or apply to each element of a vector/matrix.  For example, look at the difference between the outputs of vector dot product(*), matrix multiplication, vector power, vectorized multiplication and the sine function.

Consequently, you only need to apply vectorization when you intend the operation to be element-by-element.

Stuart

(*) The dot product produces a scalar.   [1xn] * [nx1] matrix multiplication produces a [1x1] matrix.