MATLAB: data points won't connect? - matlab

Question

I only have about two weeks of experience with programming/Matlab, so I'm just a beginner. In my code I would like to plot mu as a function of alpha. When I display mu it shows the 10 values of mu for each value of alpha. However, when I plot the graph it gives the values of mu as seperate points. But I want the points to be connected with just one line. How can I solve this problem?
n=40; %number of months
p=0.23; %probability of success
num_of_simulations=100;
s=rng; x = rand(1,n)<p;
rng(s);
hold on;
for alpha=0.01:0.01:0.1;
for i=1:num_of_simulations
x = rand(1,n)<p;
S0=5000; %initial value
Y(1)=S0*alpha; %deposit
for k=1
if x(1,1)==1;
S(1, i)=S0+2*Y(1);
else
S(1, i)=S0-Y(1);
end
end
for k=2:n
Y(k)=S(k-1, i)*alpha;
if x(1,k)==1;
S(k, i)=S(k-1, i)+2*Y(k);
else
S(k, i)=S(k-1, i)-Y(k);
end
end
Sn(i)=S(n,i); %end value for each simulations
end
mu=mean(Sn);
disp(mu);
plot(alpha,mu);
end

Answer 1

The reason your points aren't connected is because you plot each point separately. If we take a different approach and take alpha = 0.01:0.01:0.1; out of the for loop definition and then change the for loop definition to for j=1:numel(alpha) we can still loop over every element of alpha. Now we need to change each use of alpha in the loop to alpha(j) so that we are referring to the current element of alpha and not every element. Following on from this we need to change mu to mu(j). What this means is that when the entire loop has finished we have all of the values of alpha and mu stored and 1 call to plot(alpha, mu) will plot the data with the points connected as in
This also enables us to remove hold on; too as we only plot once.
I've included the complete edited code here for you to see. The changes are minuscule and should make sense.
clear all
close all
n = 40; %number of months
p = 0.23; %probability of success
num_of_simulations = 100;
s = rng;
x = rand(1, n) < p;
rng(s);
alpha = 0.01:0.01:0.1;
for j = 1:numel(alpha)
for i = 1:num_of_simulations
x = rand(1, n) < p;
S0 = 5000; %initial value
Y(1) = S0*alpha(j); %deposit
for k = 1
if x(1, 1) == 1;
S(1, i) = S0 + 2*Y(1);
else
S(1, i) = S0 - Y(1);
end
end
for k = 2:n
Y(k) = S(k-1, i)*alpha(j);
if x(1, k) == 1;
S(k, i) = S(k-1, i) + 2*Y(k);
else
S(k, i) = S(k-1, i) - Y(k);
end
end
Sn(i) = S(n, i); %end value for each simulations
end
mu(j) = mean(Sn);
disp(mu(j));
end
plot(alpha, mu);