Question about ilaplace()

2016 4 19
1 个回答
更新时间：2016 4 20
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0 个投票

The following lines:
>> syms s;
>> Fs = s^2;
>> ilaplace(Fs)
produce this output:
ans =
dirac(t, 2)
suggesting (to me) that there is a dirac() function that takes two arguments. However, for example,
>> dirac(1,2)
outputs an error ("Too many input arguments."). Can someone give me an explanation to that?
Thanks.

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回答（1 个）

Wayne King
Wayne King 2016-4-19
编辑：Wayne King 2016-4-19

0 个投票

I think you mean
dirac(2,t)
and not dirac(t,2)
There is a function in Symbolic Toolbox called dirac() that takes the following syntax
dirac(n,x)
where n is the order of the derivative. Of course derivative is understood here in the sense of distributions.
So dirac(2,t) is the 2nd derivative of the Dirac distribution with respect to the variable t.
See the reference page:
dirac

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Fausto Arinos Barbuto
编辑：Fausto Arinos Barbuto 2016-4-19
Hi Wayne;
Thanks for your reply.
dirac(t,2) is Matlab's very own output. I just copied and pasted such output into my note. On the other hand, ">> help dirac" says that dirac() is a function that takes only one argument. Too much confusion for a single function. Could that be because the Matlab version I tried is a bit too old (7.9.0 R2009b)?
Anyway, might you supply a simple and short example on how to use this symbolic Dirac function? Nothing seems to work and I'm really lost.
Walter Roberson
Walter Roberson 2016-4-19
The symbolic toolbox dirac is invoked if you have symbolic arguments. The numeric dirac is invoked if your arguments are completely numeric. For example
dirac(2, sym('1'))
compared to
dirac(2, 1)
Walter,
What you suggested did not work:
>> dirac(2, sym('1'))
Error using sym/dirac
Too many input arguments.
I must be missing something.
Walter Roberson
Walter Roberson 2016-4-20
Hmmm, try
dirac(sym('2'), sym('1'))
if that does not work then try
evalin(symengine, 'dirac', 2, 1)

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