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## Re: Inverse Laplace transform?

 From: A S Hodel Subject: Re: Inverse Laplace transform? Date: Sun, 10 Dec 2006 17:22:34 -0600

If you have the coefficients (numerical) of a rational function (poles/zeros, etc.) you can use the controls toolbox (ss, zp, tf) to convert from a state space form to transfer function. Alternatively, you can use the impulse function to get the time-domain function corresponding to a strictly proper Laplace domain transfer function.
```

On Dec 10, 2006, at 2:25 PM, Joe Koski wrote:

```
```on 12/10/06 12:31 PM, Doug Stewart at address@hidden wrote:

```
```Joe Koski wrote:
```
```on 12/10/06 10:36 AM, Doug Stewart at address@hidden wrote:

```
```Is there an inverse Laplace transform function in Octave?
Doug Stewart

```
```
Doug,

```
Check ifft at http://octave.sourceforge.net/index/index.html, or help ifft
```at the octave prompt.

Joe

```
```Thanks Joe
```
I did look there and there is nothing for Inverse Laplace transform that
```I can see.

```
I have written up a crude version that is not ready for prime time yet. I thought I would ask before I spent the time to reinvent the wheel :-)
```
```
What I have is a function ( for the controls tool box) that takes in a
```sys type transfer function.
It then uses the residue function to do the partial fraction
```
expansion.From this I form up a string that is the time representation
```of each factor.  What I am having a little difficulty with is how to
get  the string formatted nicely.

```
I have a cell array with each location holding a string that is the time
```representation of a term.
What I want to do  is take  these and form them into one long string
that has all the "+"'s and "-"'s between each term properly formated.

So any help would be appreciated.

resultstring = cell(1,1)  "+" cell(2,1) "-" cell(3,1)

is what I can't seem to do?

Thanks in advance for any help.

Doug Stewart

```
```
Doug,

```
Sorry, I was reading Fourier instead of Laplace transform. I guess I was
```just seeing the word transform. For calculation of inverse Laplace
transforms, I use Maxima, a symbolic math package, and it works well.

Sorry for the confusion.

Joe

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```