CODEWITHSUNDEEP
matlab
Budi Sutrisno
Budi Sutrisno

Reputation: 727

How to plot graph with customized axis

I apologize for asking this, I believe this is a simple task, but I don't know how to do it.

Suppose I have a formula y = (exp(-x) + x^2)/sqrt(pi(x) and I want to plot it as y versus x^2.

How does one do this?

Upvotes: 0

Views: 114

Answers (2)

Dan
Dan

Reputation: 45741

Like this:

 X = 0:0.1:5;   %// Get the x values
 x = X.^2;      %// Square them
 %// Your formula had errors, I fixed them but I could have misinterpreted here, please check
 y = (exp(-x) + x.^2)./sqrt(pi*x);   %// Calculate y at intervals based on the squared x. This is still y = f(x), I'm just calculating it at the points at which I want to plot it.

 plot(x,y) %//Plot against the square X.

At this point this is no different to having just plotted it normally. What you want is to make the tickmarks go up in values of X.^2. This does not change the y-values nor distort the function, it just changes what it looks like visually. Similar to plotting against a log scale:

set(gca, 'XTick', X.^2)  %//Set the tickmarks to be squared

The second method gives you a plot like enter image description here

edit:

Actually I think you were asking for this:

x = 0:0.1:5;
y = x.^2;   %// Put your function in here, I'm using a simple quadratic for illustrative purposes. 
plot(x.^2,y) %//Plot against the square X. Now your y values a f(x^2) which is wrong, but we'll fix that later
set(gca, 'XTick', (0:0.5:5).^2)  %//Set the tickmarks to be a nonlinear intervals
set(gca, 'XTickLabel', 0:0.5:5)  %//Cahnge the labels to be the original x values, now accroding to the plot y = f(x) again but has the shape of f(x^2)

So here I'm plotting a simple quadratic, but if I plot it against a squared x it should become linear. However I still want to read off the graph that y=x^2, not y=x, I just want it to look like y=x. So if I read the y value for the x value of 4 on that graph i will get 16 which is still the same correct original y value.

enter image description here

Upvotes: 1

am304
am304

Reputation: 13866

Here's my answer: it is similar to Dan's one, but fundamentally different. You can calculate the values of y as a function of x, but plot them as a function of x^2, which is what the OP was asking, if my understanding is correct:

x = 0:0.1:5;   %// Get the x values
x_squared = x.^2;      %// Square them
%// Your formula had errors, I fixed them but I could have misinterpreted here, please check
y = (exp(-x) + x.^2)./sqrt(pi*x);   %// Calculate y based on x, not the square of x

plot(x_squared,y) %//Plot against the square of x

As Dan mentioned, you can always change the tickmarks:

x_ticks = (0:0.5:5).^2; % coarser vector to avoid excessive number of ticks
set(gca, 'XTick', x_ticks)  %//Set the tickmarks to be squared

enter image description here

Upvotes: 0

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