In this tutorial we will deal with some common programming structures and also alternative conditionally statements. These statements exist as well in almost all high-level programming languages. In Matlab a common programming construction is a if or a switch statement. To repeat a number of statements, can be solved with a for or a while loop.

In the following examples we will see how this is implemented in Matlab, but nevertheless how good programmers we are, some mistakes will happen. This also motivates a brief view of the debugger in Matlab.

### For Loop in MATLAB

The general expression for a for-loop is:

for variable=expression
control statements
end |

for variable=expression
control statements
end

#### Example 1:

Let us write an m-file that calculates the sum: The sum to be calculated is: 1+1/2^{2}+1/3^{2}+…..+1/10^{2}.

i=1;
the_sum=0;
for i=1:10
the_sum=the_sum+1/(i^2);
end
fprintf('The sum of 10 elements gives: %f ', the_sum) |

i=1;
the_sum=0;
for i=1:10
the_sum=the_sum+1/(i^2);
end
fprintf('The sum of 10 elements gives: %f ', the_sum)

The execution of the code in Matlab command window gives: The sum of elements gives: 1.549768

The variable expression assigns a value to the loop variable, one start value and one end value, if nothing else is given assume increment 1 (for i=1:10).

The control statements can be expressed with more arbitrary expressions.

#### Example 2:

% The m-file The_sum.m calculates the five first odd elements i=1,3,5,8,9
% Below follows The_sum.m.
i=1;
the_sum=0;
disp('i the_sum')
disp('-----------')
for i=[1 3 5 8 9]
the_sum=the_sum+1/(i^2);
fprintf('%2u %7.2f \n',i,the_sum)
end |

% The m-file The_sum.m calculates the five first odd elements i=1,3,5,8,9
% Below follows The_sum.m.
i=1;
the_sum=0;
disp('i the_sum')
disp('-----------')
for i=[1 3 5 8 9]
the_sum=the_sum+1/(i^2);
fprintf('%2u %7.2f \n',i,the_sum)
end

After callling the the m-file The_sum we get:

i the_sum
------------
1 1.00
3 1.11
5 1.15
8 1.17
9 1.18 |

i the_sum
------------
1 1.00
3 1.11
5 1.15
8 1.17
9 1.18

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Matlab Tutorials | admin, July 5, 2010 8:47 am