Sunday, August 11, 2013

A Hands-on Guide to ScicosLab - Part 1

The basic calculation unit is a vector or a matrix in ScicosLab. What we get used to is a 1*1 matrix.

Define a Vector

--> 0:0.1:4*%pi

Well, the result is stored in the variable ans and the vector will be displayed hereafter. This vector is comprised of float numbers from 0 to 4π with a spacing of 0.1, they are 116 numbers, check this with the function length(). Yes, %pi is the Scicos way of pre-defining some constants. For the logarithmic natural base e, it uses %e. To stop printing results after each command, one can end it with a semi-colon(;).

Use Variables

--> a = 0:0.1:4*%pi;

Variables are type-free when being declared, so the initialization will make the variable a being a vector. Any assignment will change its content and type just like using a brand-new variable. The system preserved variable ans will be updated in the same fashion after executing every command.

--> a = sin(a);

Plot a Sine Wave

--> plot(a);

This gives you a sine wave of 2 periods.

Perform Discret Fourier Transform

--> v = dft(a,-1);
--> clf();
--> plot(v);

To check the usage of a function or related entries, use

--> apropos fourier
--> help dft

To clear the graph/figure, use the function clf(). We see in the new plotting

ScicosLab just drew the real part of frequency components, to compare with the imaginary parts, use

--> plot(imag(v), 'red');

The figure gets re-shaped and we see two spikes again. As a matter of fact, the Fourier transform of sine wave is two dirac functions.

Variables Revisited

--> browsevar
--> clear

The former gives a window of currently being-used variables, and the latter command just destroys them.

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