# matlab plot function

• May 26th 2010, 07:18 AM
AUCC
matlab plot function
Code:

```x1=-10:.1:10; y1=exp(x1) - (7*x1); plot(x1,y1);```
The graph that i get looks very wrong

How can i resolve this issue

• May 26th 2010, 07:27 AM
Laurent
Quote:

Originally Posted by AUCC
Code:

```x1=-10:.1:10; y1=exp(x1) - (7*x1); plot(x1,y1);```
The graph that i get looks very wrong

How can i resolve this issue

The graph IS correct. But give a look at the scale on the vertical axis... Problem is that for x=10, $\exp(x)$ is huge, so that we can't even distinguish $-70$ (which would be the value for x=-10, approx.) from 0.

"Solution" is to adjust the extent of the values x is assumed to take: choose x1=-10:.1:5 instead, for instance.
• May 26th 2010, 07:41 AM
AUCC
Well i didn't focus on the shape of the graph for positive values for x

For negative values of x the graph looks very very wrong

at x values lesser than zero the graph should go in the upward direction but the graph that mat-lab gives me lies on the x axis.

• May 26th 2010, 07:45 AM
Laurent
Quote:

Originally Posted by AUCC
Well i didn't focus on the shape of the graph for positive values for x

For negative values of x the graph looks very very wrong

at x values lesser than zero the graph should go in the upward direction but the graph that mat-lab gives me lies on the x axis.

That's what I said. Matlab scales the axes so that the plot fits inside the window. The values for positive x are huge, so that Matlab has to choose a very large scale (I mean, which grows very quickly). On the other hand, on such a scale, the positive slope for negative x looks horizontal because it is not very steep. Make the change I recommended, and then maybe you'll get what I mean.
• May 26th 2010, 08:03 AM
AUCC
oh thanks. Now i got it.