## introducing a new variable

### richard (view profile)

on 13 Nov 2013
Latest activity Commented on by richard

### richard (view profile)

on 14 Nov 2013

I am trying to introduce a new variable that is in terms of a variable that is known.

r''=(-b/a)*r

where r is just a row vector going from -15:15, r'' is the new variable, b&a are the unknown,real constants.

Ultimately I am trying to express a gaussian function in terms of the r=(-a/b)*r'', and take fft's of these gaussian functions.

I have tried using:

syms r'' a b

however when I am trying to take fft's, matlab is unable to do this because a, b, and r'' are syms.

I can't think of another way to introduce this new variable, maybe after the fft of the gaussian is taken? Below is the code I am using but an error comes up at the last two lines. Any help will be appreciated

```clear
syms r'' a b real
r=-15:15;
r=-(a/b)*r'';
h=gaussmf(r,[(0.5)/(2*sqrt(2*log(2))),0]);
g=gaussmf(r,[(0.1)/(2*sqrt(2*log(2))),0]);
H=fft(h);
G=fft(G);
```

## Products

No products are associated with this question.

### Vivek Selvam (view profile)

Answer by Vivek Selvam

on 13 Nov 2013

### Walter Roberson (view profile)

Answer by Walter Roberson

### Walter Roberson (view profile)

on 13 Nov 2013

I would doubt that you can use r'' as a symbol name. Try using a name that starts with a letter, and consists entirely of letters, digits, or underscores.

richard

### richard (view profile)

on 14 Nov 2013

I have changed my r'' to rr's and the last two lines are still reading out as an error. I changed my code to look life this:

```clear
syms rr a b real
rr=-15:15;
r=-(a/b)*rr;
h=gaussmf(r,[(0.5)/(2*sqrt(2*log(2))),0]);
g=gaussmf(r,[(0.1)/(2*sqrt(2*log(2))),0]);
H=fft(h);
G=fft(g);
```

I have now defined a vector for rr and I want to put r (in terms of a&b the unknown constants, as well as rr) into my gaussian.

In the end, I am wanting to find the function F=G./H, and take f=ifft(F), where f will be in terms of a&b.

MATLAB and Simulink resources for Arduino, LEGO, and Raspberry Pi