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1-Newbie

## No Topic

I am taking limit of a very basic exponential function with MC14 and I have realized it is not working properly. Am I doing something wrong with the attached file? If the coefficient of "t" has a decimal digit, it doesn't calculate it.
I have saved it in MC11 so more people can open it. However, I run it on MC14, M020. The attached pdf file is the output from MC14.
Thanks for the help.

Mark.
17 REPLIES 17
1-Newbie
(To:mark_neil2)
>the limit should be 0<, YES and for either � t and no matter the coefficient of t, whereas X*t wehere t = infty is infty. The MuPad does not obey the essential rules of calculus. This symbolic engine is not even good enough for first year calculus, not even home work. It seems that MuPad tried to imitate Maple by considering that 3.5 is a variable that could vary but by same token ignoring the X*infty = infty, an essential convention in maths. That kind of idiotics deserves a 1 m� poster "by MuPad" ! From all what was said about MuPad in this collab, it seems it was designed by "book pages" but not by the rules of symbolic algebra, especially advanced algebra.

jmg
1-Newbie
(To:mark_neil2)
Using a number with a decimal point makes a huge difference to the symbolic processor. It results in the expression being evaluated using floating point arithmetic rather than the usual exact (rational) arithmetic.

MuPad is a bit strange. Here you just need the simplify keyword to have it calculate the limit even with the decimal number.
__________________
� � � � Tom Gutman
1-Newbie
(To:TomGutman)
On 7/21/2009 5:13:06 PM, Tom_Gutman wrote:
>Using a number with a decimal
>point makes a huge difference
>to the symbolic processor. It
>results in the expression
>being evaluated using floating
>point arithmetic rather than
>the usual exact (rational)
>arithmetic.
>
>MuPad is a bit strange. Here
>you just need the simplify
>keyword to have it calculate
>the limit even with the
>decimal number.
>__________________
>� � � � Tom Gutman

The reason I am taking the limit is that I have a function with sin and cos terms and some other terms of sin and cos but multiplied by exponential terms with the power coefficient always being negative. See the formula in the attached file as an example. I am interested in taking the first two terms and dropping the last two terms. What other way can be used to accomplish this?
Thanks.

Mark
1-Newbie
(To:mark_neil2)
There won't be much of a limit out that function.
>I am interested in taking the first two terms and dropping the last two terms<<br> Hard to do as your function has only 3 terms !

jmG
1-Newbie
(To:ptc-1368288)
On 7/21/2009 7:38:07 PM, jmG wrote:
>There won't be much of a limit
>out that function.
>>I am interested in taking the first two terms and dropping the last two terms<<br> >Hard to do as your function
>has only 3 terms !
>
>jmG
__________

i.e: 3 algebraic terms.

1-Newbie
(To:ptc-1368288)
On 7/21/2009 7:48:29 PM, jmG wrote:
>On 7/21/2009 7:38:07 PM, jmG wrote:
>>There won't be much of a limit
>>out that function.
>>>I am interested in taking the first two terms and dropping the last two terms<<br> >>Hard to do as your function
>>has only 3 terms !
>>
>>jmG
>__________
>
>i.e: 3 algebraic terms.
>
>
>

There are 4 functions summed in my file. Two with sin and cos and the other two are with sin and cos multiplied by exponential fucntions.

Plotting the function is no big deal and I know that the exponential terms are insignificant. That is why I want to get rid of them. I will apply some symbolic keywords later on to out(t) function but before I do that I want to get rid of the terms in out(t) with exponential terms. I can manually select those terms and copy/paste into a different function. But I try to avoid manual operation. I hope it is clear now what I am trying to do...

Mark.
1-Newbie
(To:mark_neil2)
Limits wouldn't help anyway. While the terms with the exponentials have a limit of zero (and so drop out), the sine and cosine terms don't. Exactly how the sine and cosine are treated differ between Mathcad versions. MC13 attempts to get a limit, and gets something more or less reasonable (albeit of questionable utility -- what happens if you try to use that is subsequent calculations?), but when applied to out gets it quite wrong.

In MC14 you can get rid of the exponential terms by using substitution. Score a rare victory for MuPad.
__________________
� � � � Tom Gutman
1-Newbie
(To:TomGutman)
On 7/21/2009 8:43:31 PM, Tom_Gutman wrote:
>Limits wouldn't help anyway.
>While the terms with the
>exponentials have a limit of
>zero (and so drop out), the
>sine and cosine terms don't.
>Exactly how the sine and
>cosine are treated differ
>MC13 attempts to get a limit,
>and gets something more or
>less reasonable (albeit of
>questionable utility -- what
>happens if you try to use that
>is subsequent calculations?),
>but when applied to out gets
>it quite wrong.
>
>In MC14 you can get rid of the
>exponential terms by using
>substitution. Score a rare
>__________________
>� � � � Tom Gutman

Substituting e with inf solves my problem. Thanks, Tom.

Mark.
1-Newbie
(To:mark_neil2)
On 7/21/2009 8:56:29 PM, mark_neil wrote:
>On 7/21/2009 8:43:31 PM, Tom_Gutman
>wrote:
>>Limits wouldn't help anyway.
>>While the terms with the
>>exponentials have a limit of
>>zero (and so drop out), the
>>sine and cosine terms don't.
>>Exactly how the sine and
>>cosine are treated differ
>>MC13 attempts to get a limit,
>>and gets something more or
>>less reasonable (albeit of
>>questionable utility -- what
>>happens if you try to use that
>>is subsequent calculations?),
>>but when applied to out gets
>>it quite wrong.
>>
>>In MC14 you can get rid of the
>>exponential terms by using
>>substitution. Score a rare
>>__________________
>>� � � � Tom Gutman
>
>
>Substituting e with inf solves my
>problem. Thanks, Tom.
>
>Mark.

Tom,
Although replacing e with inf works with MC14, it doesn't work with MC13. Do you have a suggestion to eliminate the exponential terms in MC13? Thanks.

Mark.
1-Newbie
(To:mark_neil2)
In MC13 you can substitute for exp. But, due to a bug in MC13, not directly. Only through a function definition.
__________________
� � � � Tom Gutman
1-Newbie
(To:TomGutman)
On 7/23/2009 3:45:14 PM, Tom_Gutman wrote:
>In MC13 you can substitute for
>exp. But, due to a bug in
>MC13, not directly. Only
>through a function definition.
>__________________
>� � � � Tom Gutman

It is working, thanks for the suggestion.

Mark
1-Newbie
(To:TomGutman)
On 7/21/2009 8:43:31 PM, Tom_Gutman wrote:
>In MC14 you can get rid of the
>exponential terms by using
>substitution. Score a rare
This approach doesn't seem to work with Mathcad 2001i. But as the attached file demonstrates, the undocumented Maple function SELECT can be used with Mathcad 2001i to strip off the exponential terms.

1-Newbie
(To:schneidrax)
On 7/21/2009 9:32:32 PM, schneidrax wrote:
>On 7/21/2009 8:43:31 PM, Tom_Gutman
>wrote:
>>In MC14 you can get rid of the
>>exponential terms by using
>>substitution. Score a rare
>This approach doesn't seem to work with
>Mathcad 2001i. But as the attached file
>demonstrates, the undocumented Maple
>function SELECT can be used with Mathcad
>2001i to strip off the exponential
>terms.
>
>___________________________________

The user must be very ingenious to use this function on two counts: 't' and the "decimal figures". And it all depends upon the original function in the Laplace domain. Sorry, but I don't trust the Laplace construct, just can't see where it could come from. Such a puzzle should be sourced in order to check where the error is. The Laplace algebra is specific and easy to plunge.

Metafile added for all to enjoy this curiosity.

jmG

1-Newbie
(To:mark_neil2)
>I am taking limit of a very basic exponential function<<br>
You mean the limit of this function ?

jmG
1-Newbie
(To:ptc-1368288)
That long monkey business equation for Phi !
Deserves no comment especially after some previous remarks I made. This thread would gain some exposure, I can see what the collab is trying to do..... Sorry for your Phi but negative time does not exist, and no system under oscillation can be controlled. The objective in control strategies is to avoid oscillations, that's why we model them but everything here is out of the blue. There are many underlying interpretations and the other problem is whatever Mathcad 11 could do might be rejected by 14.

You might conclude useful to plot your own creation.

jmG
1-Newbie
(To:ptc-1368288)
On 7/21/2009 11:58:56 PM, jmG wrote:
>>I am taking limit of a very basic exponential function<<br> >
>You mean the limit of this
>function ?
>

No, not this function. I meant the function in my first message in this thread: e^(-3.5*t). I expected Mathcad to display the result as zero as t goes to inf. Limit was not the right approach anyways for what Iwas trying to do. Tom's suggestion solved my problem. Thanks to everyone who spent time for helping me with this.

Mark.
1-Newbie
(To:mark_neil2)
>I expected Mathcad to display the result as zero as t goes to inf. < Yes and is quite conventional in symbolic maths, but MuPad is a low symbolic algebra. All has been explained. exp(� t--> infty) has only one limit that Mupad should take from books.

jmG
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