if/elseif/else
Execute statements if condition is true
Syntax
if expression
statements
elseif expression
statements
else
statements
end
Description
if expression, statements, end evaluates an expression, and
executes a group of statements when the expression is true.
elseif and else are optional, and execute statements only when
previous expressions in the if block are false.
An if block can include multiple elseif statements.

Example 1

>> a = 1;
>> if a==1
disp('Hello World')
end
Hello World

Example 2

>> b = 10;
>> if b == 10
disp('Value is exactly 10')
else
disp('Value is not 10, try again')
end
Value is exactly 10

>> b = 5;
>> if b == 10
disp('Value is exactly 10')
else
disp('Value is not 10, try again')
end
Value is not 10, try again

Example 3

Here is a sample script which demonstrates more complex flow control.

X=ones(10);
if length(X)>500
disp('That is a long vector')
elseif length(X)==1
X=ones(500);
fprintf('I made your vector %d elements long\n',length(X))
else
disp('Your vector is sufficiently long')
end

Video explanation:

Example 4

This example for IF statements and For loops comes directly from the Matlab documentation on IF.

% Preallocate a matrix
nrows = 10;
ncols = 10;
myData = ones(nrows, ncols);
% Loop through the matrix
for r = 1:nrows
for c = 1:ncols
if r == c
myData(r,c) = 2;
elseif abs(r - c) == 1
myData(r,c) = -1;
else
myData(r,c) = 0;
end
end
end
imagesc(myData)

Video explanation:

Example applied to Yellowstone Earthquakes

This example applies to a question from last class: How to control plotting of text.

if length(locations)~=0
s = sprintf('%2.1f',mean_depth);
text(long, lat, s);
end