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05-07-2013
02:25 PM

05-07-2013
02:25 PM

In the highlighted integration, I want to tell MathCAD that the c is constant, but have not been able to figure out how to do so. I've seached some, but no luck.

Thanks

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05-07-2013
04:53 PM

05-07-2013
04:53 PM

No need to tell Mathcad so, Mathcad's symbolic treats c as a constant (for MC's numeric c is velocity of light)

I guess you are puzzled as of the huge expression you get in evaluating that integral while you would have expected something like

But while Mathcad treats c as a constant it has to consider all possibilities, c could be -v1, it could be complex, etc.

So Mathcad gives you the results with a lot of if's to cope for every eventuality.

Your function has a vertical asymptote at v=-c, so the bounderies of your definite integral have to be both at the left or both at the right of -c, otherwise the integral would have to be infinity. Obviously c must not be -v1 or -v2 or you would get a divison by zero.

Replace c by a number and see that Mahcad still has some ifs, but less as with an unknown c.

You might try to use assume to get a more meaningful result. Unfortunately "assume" very often does not work as expected. E.g. "assume, -c<v1<v2" should do the job, but doesn't.

EDIT: Interestingly enough "assume, -c < v1" does the job - thats crazy!

In fact "simplify" would not be necessary here, typing it is just a reflex 😉

5 REPLIES 5

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05-07-2013
03:13 PM

05-07-2013
03:13 PM

Re: How to tell MathCAD something is constant

c:=c

and than the integral

PS

May be this will be interesting for you

http://twt.mpei.ac.ru/TTHB/2/tdceng.html

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05-07-2013
04:53 PM

05-07-2013
04:53 PM

No need to tell Mathcad so, Mathcad's symbolic treats c as a constant (for MC's numeric c is velocity of light)

I guess you are puzzled as of the huge expression you get in evaluating that integral while you would have expected something like

But while Mathcad treats c as a constant it has to consider all possibilities, c could be -v1, it could be complex, etc.

So Mathcad gives you the results with a lot of if's to cope for every eventuality.

Your function has a vertical asymptote at v=-c, so the bounderies of your definite integral have to be both at the left or both at the right of -c, otherwise the integral would have to be infinity. Obviously c must not be -v1 or -v2 or you would get a divison by zero.

Replace c by a number and see that Mahcad still has some ifs, but less as with an unknown c.

You might try to use assume to get a more meaningful result. Unfortunately "assume" very often does not work as expected. E.g. "assume, -c<v1<v2" should do the job, but doesn't.

EDIT: Interestingly enough "assume, -c < v1" does the job - thats crazy!

In fact "simplify" would not be necessary here, typing it is just a reflex 😉

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05-07-2013
09:25 PM

05-07-2013
09:25 PM

Re: How to tell MathCAD something is constant

Werner Exinger wrote:

No need to tell Mathcad so, Mathcad's symbolic treats c as a constant (for MC's numeric c is velocity of light)

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05-08-2013
11:11 PM

05-08-2013
11:11 PM

Re: How to tell MathCAD something is constant

That is an awesome site. Inspires me to go learn a little Russian.

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05-09-2013
03:55 AM

05-09-2013
03:55 AM

Re: How to tell MathCAD something is constant

Samuel Bernstel wrote:

That is an awesome site. Inspires me to go learn a little Russian.

Thanks!

I try to translate the site into English but...

Can You help me?

Point me please pages of the site and I will translate its.

Some my article in English in this area (themogynamic + Mathcad) You can see here http://twt.mpei.ac.ru/ochkov/work2_eng.htm

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