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

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.