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Sergey15-Moonstone
15-Moonstone
November 15, 2022
Solved

Partial derivative evaluation

Hello!

 

Would you, please, point out why I can't evaluate the symbolic expression of of the r(x,0) function while d(0) is possible to evaluate? Those are identical expressions but by some reason Mathcad evaluates correctly only one of them. It is inconvinient to introduce new function such as d(t) to compute r(x,t). I marked equations by the blue colour.

 

Best regards,

Sergey

LucMeekesAnswer
23-Emerald IV
November 15, 2022

You have a function r defined as:

LucMeekes_1-1668545266829.png

and define a function d with:

LucMeekes_2-1668545421983.png

and wonder why:

LucMeekes_0-1668545190689.png

That is because Prime doesn't look back to the definition of r, to check and see if it was defined with a parameter t or not. It sees that r(x,0) is NOT a function of t, so the result of the (partial) derivative is 0.

Note that:

LucMeekes_3-1668545444548.png

(I replaced t with z...) which means that fun is essentially the same function as your function d.

In order to get:

LucMeekes_4-1668545506567.png

be the same as the direct form through the partial derivative, you have to:

LucMeekes_5-1668545550836.png

Success!
Luc

 

 

 

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2 replies

LucMeekes23-Emerald IVAnswer
23-Emerald IV
November 15, 2022

You have a function r defined as:

LucMeekes_1-1668545266829.png

and define a function d with:

LucMeekes_2-1668545421983.png

and wonder why:

LucMeekes_0-1668545190689.png

That is because Prime doesn't look back to the definition of r, to check and see if it was defined with a parameter t or not. It sees that r(x,0) is NOT a function of t, so the result of the (partial) derivative is 0.

Note that:

LucMeekes_3-1668545444548.png

(I replaced t with z...) which means that fun is essentially the same function as your function d.

In order to get:

LucMeekes_4-1668545506567.png

be the same as the direct form through the partial derivative, you have to:

LucMeekes_5-1668545550836.png

Success!
Luc

 

 

 

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    Sergey15-MoonstoneAuthor
    15-Moonstone
    November 15, 2022

    Thanks a lot, Luc!

     

     

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