## Matlab Tutorial 7: Common Programming Structures and Conditional Statements

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```

#### Example 1:

Let us write an m-file that calculates the sum: The sum to be calculated is: 1+1/22+1/32+…..+1/102.

```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
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## Matlab Tutorial 5: Linear Equations

In this Matlab tutorial we will deal with linear equations, the least square method, condition numbers over & under-determined equations.

Let’s start with an example.

Example 1

We have an equation system with three unknown variables and three equations. What will be the solution to the system below?

3w-2y+4z=8
5w+8y-6z=-5
9w-2y+7z=-17

Assume a matrix A containing the coefficients multiplied with x, y and z, and a vector with the numbers on the right-hand side of the equations. We can thus rewrite our equations as:

AX=b , where X contains the unknown (w, y and z), A and b are shown below.

```b= A= 8 3 -2 4 -5 5 8 -6 -17 9 -2 7```

How will we find the solution?

`>> X=inv(A)*b`

or

`>> X=A\b`

both gives a correct answer. The last method produces a Gaussian elimination if A is a quadratic matrix. In our case X becomes:

```X= -36.7778 71.2778 65.2222```

This is no exact solution, only an approximation. Try also a specific command: Read more »