Sunday, January 16, 2011

Basic commands and syntax in MATLAB

    We will speak about Basic commands and syntax in MATLAB to show how we can write code in it .

    If you type in a valid expression and press Enter, MATLAB will immediately execute it and return the result.

>> 2+2
ans =
           4

>> 4ˆ2

ans =
           16

>> sin(pi/2)

ans =
           1

>> 1/0


Warning: Divide by zero.

ans =
            Inf

>> exp(i*pi)

ans =
            -1.0000 + 0.0000i

       Notice some of the special expressions here: pi for π, Inf for ∞, and i for √−1. Another is NaN, which stands for not a number. NaN is used to express an undefined value. For example,

>> Inf/Inf

ans =
            NaN

You can assign values to variables.

>> x = sqrt(3)

x =
          1.7321

>> 3*z

??? Undefined function or variable ’z’.

      Observe that variables must have values before they can be used. When an expression returns a single result that is not assigned to a variable, this result is assigned to ans, which can then be used like any other variable.

>> atan(x)

ans =
            1.0472

>> pi/ans

ans =
            3
 
      In floating-point arithmetic, you should not expect “equal” values to have a difference of exactly zero. The built-in number eps tells you the maximum error in arithmetic on your particular machine. For simple operations, the relative error should be less than this number. For instance,

>> exp(log(10)) - 10

ans =
            1.7764e-15

>> ans/10

ans =
            1.7764e-16

>> eps

ans =
             2.2204e-16

Here are a few other demonstration statements.

>>  %  This is a comment.
>>  x  =  rand(100,100) ;  %  ;  means "don’t print out"
>>  s  =  ’Hello world’ ;  %  quotes enclose a string
>>  t   =  1 + 2 + 3 + ...

   4 + 5 + 6                       % ... continues a line

t =
        21

     Once variables have been defined, they exist in the workspace. You can see what’s in the
workspace from the desktop or by using

>> who
Your variables are:

ans      s     t    x

How to  save  work ?

      If you enter save myfile, all the variables in the workspace will be saved to a file myfile.mat
in the current directory. Later you can use load myfile to recover the variables.

      If you right-click in the Command History window and select “Create M-File. . . ”, you can
save all your typed commands to a text file. This can be very helpful for recreating what you have done.

Q:

Evaluate the following mathematical expressions in MATLAB

----   tanh(e)   


----   log10 (2)

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