MATLAB Short Course 3: Flow control MATLAB functions

Contents

if

n = 1;
if (n==2)
    print("n = 2");
end

% if-else
if (n==2)
    print("n = 2");
else
    print("n is not 2");
end

branching using "if" to get the sign of x

x = randn(1)
% get the sign of x
if (x>0)
    s = 1;
elseif (x==0)
    s = 0;
else   % alternatively: elseif (x<0)
    s = -1;
end
s

x =

    0.3192


s =

     1

branching using "if" to get the absolution value

% the absolute value (same as "abs" in matlab)
x = randn(1)
if (x>0)
    x = x;
elseif (x==0)
    x = 0;
else
    x = -x;
end
x

x =

    0.3129


x =

    0.3129

alternative simplified version for absolute value

x = randn(1)
if (x<0)
    x = -x;
end
x

x =

   -0.8649


x =

    0.8649

for loop

for variable = start_value:step:end_value

% calculate the sum of integers from 1 to 100
S = 0;
for n = 1:1:100
    S = S+n;
end
S

S =

        5050

sum of inverse squares

S = 1 + 1/2^2 + 1/3^2 + ....

format compact
format long
N = 10000;
S = 0;
for n = 1:N
    S = S+1/n^2;
end
[S; pi^2/6]

ans =
   1.644834071848065
   1.644934066848226

"while" loop

sum inverse squares using while loop

N = 10000;
n = 1;
S = 0;
while (n<=N)
    S = S + 1/n^2;
    n = n+1;
end
S

% Another version, when "n = n+1" is executed first
N = 10000;
S = 0;
n = 0;
while (n < N)
    n = n+1;
    S = S + 1/n^2;
end
S

% yet another version using "break"
N = 10000;
S = 0;
n = 1;
while (1)
    S = S + 1/n^2;
    n = n+1;
    if (n==N+1)
        break;
    end
end

S =
   1.644834071848065
S =
   1.644834071848065

loop can be stop using "break" or "continue"

k = 1;
while (1)
    k = k + 1;
    if (k>10)
        break; % break and stop the loop
    end
end
k

k =
    11

print all prime factors, if n is composite

for n = 2:20
    if (isprime(n))
        continue; % continue to the next loop, and forget the rest (inside the loop)
    end
    pf = factor(n);
    disp(['The prime factors of ' num2str(n) ' is ' num2str(pf)]);
end

The prime factors of 4 is 2  2
The prime factors of 6 is 2  3
The prime factors of 8 is 2  2  2
The prime factors of 9 is 3  3
The prime factors of 10 is 2  5
The prime factors of 12 is 2  2  3
The prime factors of 14 is 2  7
The prime factors of 15 is 3  5
The prime factors of 16 is 2  2  2  2
The prime factors of 18 is 2  3  3
The prime factors of 20 is 2  2  5

anonymous MATLAB functions (for simple ones)

myfun = @(t) sqrt(1+t.^2);

general MATLAB functions (for complicated ones)

% save the function as "myfun1.m"
% you can call it like
% y = sin(1) or y = sin(linspace(0,2*pi,101))

% function y = myfun1(x)
% y = sqrt(1+x.^2);

Published with MATLAB® R2023a