Statements and macros¶

Statements describe algorithmic actions that can be executed. There are two different types of control statements, conditional and repetitive. The first group defines conditional jumps whereas the latter one defines repetition until a conditional statement is fulfilled. Macros are used to define new functions to the MATLAB or CALFEM structure, or to store a sequence of statements in an .m-file.

Control statements¶

`if`	Conditional jump
`for`	Initiate a loop
`while`	Define a conditional loop

Macros and Functions¶

`function`	Define a new function
`script`	Store a sequence of statements

if¶

Purpose:: Conditional jump.
Syntax:

if condition
    statements
elseif condition
    statements
else
    statements
end

Description:

The if statement allows conditional execution of code blocks. The condition is evaluated and if true (nonzero), the corresponding statements are executed.

Examples:

Simple if statement:

if x > 0
    y = sqrt(x);
else
    y = 0;
end

Multiple conditions:

if x > 0
    result = 'positive';
elseif x < 0
    result = 'negative';
else
    result = 'zero';
end

Note:

In MATLAB, any nonzero value is considered true, and zero is false.

for¶

Purpose:: Initiate a loop.
Syntax:

for variable = expression
    statements
end

Description:

The for loop repeats statements for each value in the expression. The variable takes on each value from the expression in sequence.

Examples:

Simple counting loop:

for i = 1:10
    fprintf('Iteration %d\n', i);
end

Loop over array elements:

A = [1, 4, 9, 16];
for element = A
    disp(element);
end

Nested loops:

for i = 1:3
    for j = 1:3
        A(i,j) = i + j;
    end
end

Note:

The loop variable takes on the values column by column if the expression is a matrix.

while¶

Purpose:: Define a conditional loop.
Syntax:

while condition
    statements
end

Description:

The while loop repeats statements as long as the condition remains true (nonzero).

Examples:

Simple while loop:

i = 1;
while i <= 10
    fprintf('Count: %d\n', i);
    i = i + 1;
end

Convergence loop:

error = 1;
tolerance = 1e-6;
while error > tolerance
    % ... computation ...
    error = abs(new_value - old_value);
end

Note:

Be careful to ensure the condition eventually becomes false to avoid infinite loops.

function¶

Purpose:: Define a new function.
Syntax:

function [output1, output2, ...] = function_name(input1, input2, ...)
    statements
end

Description:

The function keyword defines a new function with specified inputs and outputs. Functions should be saved in .m files with the same name as the function.

Examples:

Simple function:

function y = square(x)
    y = x^2;
end

Multiple inputs and outputs:

function [sum_val, diff_val] = add_subtract(a, b)
    sum_val = a + b;
    diff_val = a - b;
end

Function with no outputs:

function plot_data(x, y)
    figure;
    plot(x, y);
    xlabel('x');
    ylabel('y');
end

Note:

MATLAB functions must be saved in .m files. The filename should match the function name.

script¶

Purpose:: Store a sequence of statements.
Syntax:

% filename: my_script.m
% This is a script file
statements

Description:

Scripts are .m files that contain a sequence of MATLAB statements. They execute in the base workspace and can access and modify variables there.

Examples:

Simple script (saved as analysis.m):

% Analysis script
load data.mat;
results = process_data(data);
plot(results);
save results.mat results;

Script with calculations:

% Calculate beam deflection
L = 10;  % beam length
E = 200e9;  % Young's modulus
I = 1e-4;  % moment of inertia
q = 1000;  % distributed load

% Maximum deflection
w_max = q * L^4 / (8 * E * I);
fprintf('Maximum deflection: %.2e m\n', w_max);

Note:

Scripts share the workspace with the command line. Variables created in scripts remain accessible.