Here's the vectorized form:
rng(0, 'Twister');
a = -1;
b = 3;
x = randi([a, b], 100, 1);
y = (x.^3) - sin(x + (pi/2)) + cos(2*x).^2;
plot(x, y)
See comments to understand how to fix your for-loop-version of this:
%r = (b-a).*rand(100,1) + a; this can be replaced with randi
%pi = 3.14; don't override pi, which is Matlab constant for pi
y = zeros(size(r)); %preallocate y to improve speed
for x = r % In common practice, the for loop counter should be a vector of integers, EX k = 1:numel(r).
% Then in your code, you refer to r(k) instead of x.
% With your current x=r, you'll get ERROR: Index must be a positive integer or logical.
% Why? because if x(1) = 0.343, Matlab cannot access the 0.343th element of y in y(x) = ...
%Note: y(x) should be y(k) instead, where k is the integer for-loop counter.
y(x) = (x.^3) - sin*(x + (pi/2)) + cos.^2*(2*x); %cannot do sin*(...) or cos.^2(...)
end
plot(y(x)) %Specify the x and y to plot.
%Currently, this will give you Index Error or it'll plot 1 point since x is 1 value.
