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KarstenJ4-Participant
4-Participant
December 21, 2021
Solved

newbie question, functions

Prime 7

KarstenJ_0-1640095803272.png

I am trying to calculate volume of a cone as a function, in steps of 0.3 meters.
I'm not sure what I'm doing wrong.
can someone enlighten me?

 

thanks in advance

Werner_E
Werner_EAnswer
25-Diamond I
December 21, 2021

From what I had seen in the sheet I assumed that only cones with a ratio of r : h = 2.5 : 6 should be considered with h running up to 6m.

If you should be able to choose r and h independently of each other, then I would rather define a function in both variables.

The picture shows how to get the values seen in Stuarts screen shot. r is the vector you already defined and while vectorizing is not mandatory here, I still think it's a good habit to do so.

Werner_E_0-1640102492755.png

 

 

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4 replies

Werner_E
Werner_E25-Diamond I
25-Diamond I
December 21, 2021

You were running into Primes infamous autolabelling feature.

Look closely at t"he "h" on the RHS of the definiton of f(h). You'll notice its coloured green like the symbol pi. That means its labelled as being a constant.

There is a predefined constant h built into Prime:

Werner_E_0-1640097056049.png

and thats the reason for the strange result you see.

Manually label that h as being a variable

AND

delete the "f(h):=" because you obviously don't want to define a function

AND

vectorize the expression

and you should see what you expect.

Werner_E_1-1640097488558.png

 

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    Werner_E
    Werner_E25-Diamond I
    25-Diamond I
    December 21, 2021

    If you want to define a function and also want to explicitly use a variable r in your formula, you could do it that way:

    Werner_E_2-1640097682153.png

    Again you have to vectorize the function call!

     

    Note that you defined h as a range but you turned it into a vector (by using the undocumented trick to immediately evaluate after the definition).

    Thats the reason you have to use vectorization also when you plot the function (left plot; plotting one vector over the other)

    If you define a range (like hh in the plot to the right), you don't need to vectorize

    Werner_E_3-1640098024879.png

     

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      StuartBruff23-Emerald V
      23-Emerald V
      December 21, 2021
      @KarstenJ wrote:

      Prime 7

      KarstenJ_0-1640095803272.png

      I am trying to calculate volume of a cone as a function, in steps of 0.3 meters.
      I'm not sure what I'm doing wrong.
      can someone enlighten me?

       

      And here's an additional, slightly different version to Werner's.

       

      2021 12 21 d.png

       

      2021 12 21 e.png

       

      Stuart

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        Werner_E
        Werner_E25-Diamond IAnswer
        25-Diamond I
        December 21, 2021

        From what I had seen in the sheet I assumed that only cones with a ratio of r : h = 2.5 : 6 should be considered with h running up to 6m.

        If you should be able to choose r and h independently of each other, then I would rather define a function in both variables.

        The picture shows how to get the values seen in Stuarts screen shot. r is the vector you already defined and while vectorizing is not mandatory here, I still think it's a good habit to do so.

        Werner_E_0-1640102492755.png

         

         

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