# Evans function invalid index error

**URL:** <https://scilab.discourse.group/t/evans-function-invalid-index-error/773>\
**Category:** Modeling and simulation\
**Created:** [December 24, 2024, 3:15pm UTC](https://scilab.discourse.group/t/evans-function-invalid-index-error/773 "2024-12-24T15:15:36Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![anwerified](https://avatars.discourse-cdn.com/v4/letter/a/f14d63/32.png) [@anwerified](https://scilab.discourse.group/u/anwerified)\
**Post date:** [December 24, 2024, 3:15pm UTC](https://scilab.discourse.group/t/evans-function-invalid-index-error/773/1 "2024-12-24T15:15:36Z")

</div>

```auto
s = poly(0, 's');
n1=(s+2); 
d1=(s+3)(s^2+2*s+2); 
h1= syslin('c', n1,d1);
disp(h1);
evans(h1,50);

```

there is no error, but the graphic window number 0 is blank.

---

<div class="post-metadata">

**Author:** ![mottelet](https://yyz2.discourse-cdn.com/free1/user_avatar/scilab.discourse.group/mottelet/32/13_2.png) [@mottelet](https://scilab.discourse.group/u/mottelet)\
**Post date:** [January 6, 2025, 12:44pm UTC](https://scilab.discourse.group/t/evans-function-invalid-index-error/773/2 "2025-01-06T12:44:50Z")

</div>

Hello,

The third line yields an error

```auto
--> s = poly(0, 's');

--> n1=(s+2); 

--> d1=(s+3)(s^2+2*s+2); 

Invalid index.

```

because you are missing a multiplication sign. By fixing it

```scilab
s = poly(0, 's');
n1=(s+2); 
d1=(s+3)*(s^2+2*s+2); 
h1= syslin('c', n1,d1);
disp(h1);
evans(h1,50);

```

you get what you expected:  
 ![disc](https://global.discourse-cdn.com/free1/uploads/utc/original/1X/f4f9037318f734855c5d537a754231379057c8da.svg)