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#1 baltoche

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Posted 20 January 2017 - 12:44 PM

Dear All,

 

I'm trying to find a primitive of f(x)=cos(-Asin(x)) where A is a constant number.

I've tried Wolfram but unsuccessfully. An approximate function of this primitive would also be welcome.

 

Thanks for your help !

 

Kind Regards.


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#2 studiot

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Posted 20 January 2017 - 12:58 PM

Would a numerical integration method not do nicely?


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#3 HallsofIvy

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Posted 20 January 2017 - 01:35 PM

  Wolfram did not work because the primitive of this function is not an "elementary function" (so cannot be written in terms of trig functions, exponentals, logs, etc.).


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#4 baltoche

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Posted 23 January 2017 - 07:51 PM

I know the values between whom I need to integrate this function, but it does not solve my issue... Regarding numerical methods (calculating a rough surface for instance), I cannot do it since my final integral will be a function of A.

If the answer is not an elementary function, is there a way to approach it ?

 

Thanks in advance.


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#5 studiot

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Posted 23 January 2017 - 09:26 PM

Well  numerical integration will just give you a numerical area, and I suppose that you want a plot of the primitive?

 

If you differentiate your equation that will turn it into a differential equation.

You can then create the plots by one of several numerical methods starting from the (presumably known) boundary conditions.

 

Edit A thought occurred to me

 

When you wrote this

 

 

 

I'm trying to find a primitive of f(x)=cos(-Asin(x)) where A is a constant number.

 

Did you mean the formula is the derivative of the function?

 

That is did you mean f'(x)=cos(-Asin(x)) ?

 

In which case you already have a differential equation to work on.


Edited by studiot, 23 January 2017 - 11:42 PM.

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#6 baltoche

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Posted 5 February 2017 - 01:10 PM

Hello Studiot,

 

Thanks for your kind contribution. Ideally, I'm after a function of A in order to plot it, knowing that I know between what values (O and Pi) I need to integrate this function. Actually, I asked for the primitive in order to calculate the integral, which is also a function of A, and this is the one I'd like to plot.

 

For your information, this primitive/integral is needed too solve Bessel's equation and function.

 

I'm sorry for the poor quality of my English.

 

Kind Regards.


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