Question

I would like to plot the shifted logistic function as shown from Wolfram Alpha.

In particular, I would like the function to be of the form

y = exp(x - t) / (1 + exp(x - t))

where t > 0. In the link, for example, t is 6. I had originally tried the following:

x = 0:.1:12;
y = exp(x - 6) ./ (1 + exp(x - 6));
plot(x, y);
axis([0 6 0 1])

However, this is not the same as the result from Wolfram Alpha. Here is an export of my plot.

I do not understand what the difference is between what I am trying to do here vs. plotting shifted sin and cosine functions (which works using the same technique).

I am not completely new to Matlab but I do not usually use it in this way.

Edit: My values for x in the code should have been from 0 to 12.

Answer 1

fplot takes as inputs a function handle and a range to plot for:

>> fplot(@(x) exp(x-6) / (1 + exp(x-6)), [0 12])

The beauty of fplot in this case is you don’t need to spend time calculating y-values beforehand; you could also extract values from the graph after the fact if you want (by getting the line handle‘s XData and YData properties).