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Scilab Examples – 2D plots

This is a practical approach to plots in Scilab. Several examples are shown to explore the capabilities of this software. After each line of code is explained, we show the result produced.

Simplest forms

Function plot2d plots a set of 2D curves. If you are familiar with the Matlab plot syntax, you could use function plot. If x and y are vectors, plot2d(x, y, <opt_args>) plots vector y versus vector x. x and y vectors must have the same size.

/ your x-values
x = 0 : .1 : 10*%pi;
/ your function
y = x .* cos(x);
/ Plot as used in Matlab
plot(x, y)
/ Add title, labels and legend
title('x * cos(x)')
xlabel('x'); ylabel('y');
legend('y = x * cos(x)');

Simplest form of a Scilab Plot

/ plot with captions and given tics + style
/ your x-values
x = [0 : 0.1 : 2*%pi]';
plot2d(x, [sin(x) sin(2*x)], [2, 5],...
leg = "sin(x)(2x)", nax = [2, 5, 1, 5],...
rect = [0, -1, 2*%pi, 1])

/ [2, 5] means lines in blue (2) and red (5)
/ leg = "sin(x)(2x)" are the legends of the lines
/ nax = [2, 5, 1, 5] are the tics and subtics of the
/ and
/ axis
/ rect = [0, -1, 2*%pi, 1] are the bounds of the axis,
/ from (0, -1) to (2pi, 1).


A Scilab Example showing two lines on the same window



Logarithmic Axis – Plots


/ your variables
t = linspace(0, 2*%pi, 300);
x = exp(-t);
y = t;
/ Use the logflag option to define logarithmic or normal axis
/ n for normal, l for logarithmic.
plot2d(x, y, logflag = "ln");
/ Use xgrid to add a grid on your current figure
xgrid;

Scilab Plot showing logarithmic axis

/ new figure window with scf
scf(); plot2d(t, exp(t), logflag = "nl"); xgrid;

Scilab Example showing vertical log axes

/ Both axis are logarithmic now
scf(); plot2d(exp(t), 50 + exp(2*t), logflag = "ll") ; xgrid

Scilab Plot with two logarithmic axis



Polar Plots

polarplot - Plot polar coordinates
polarplot(theta, rho, <opt_args>)

/ your variable
t = linspace(0, 2*%pi, 100);
/ your polar function
r = sqrt(abs(2 * cos(5*t)));
/ Plot in polar coordinates
polarplot(t, r);

Scilab - polar plot

Polar Plots in Matlab



Histograms in Scilab

histplot - plot a histogram
histplot(bins, data, <opt_args>)

/ Define your data or get it somehow
y = 10 * rand(500, 1);
/ Create the histogram. The 5 at the beginning means 5 bins.
/ The 2 at the end means lines in blue.
histplot(5, y, 2)

histograms in Scilab

Histograms in Matlab


Pie Plots


pie - draw a pie
pie(x [, sp [,txt]])

x is a scalar or a vector of real, positive numbers.
sp is a real scalar or vector.
txt means a cell or a vector of strings.

pie([1 3 4 5], [1 0 1 0],...
["Part1 Exp.","Part2","Part3 Exp.", "P4"]);

/ [1 3 4 5] is the number and size of sectors
/ [1 0 1 0], 1 for exploded sector, 0 for nonexploded
/"Part1 Exp.","Part2","Part3 Exp.", "P4"] is the associated
/ text

Pie Plot in Scilab

Pie Plots in Matlab



Stems – Vertical lines

plot2d3 - 2D plot (vertical bars)
plot2d3([logflags,] x,y,[style,strf,leg,rect,nax])
plot2d3(x,y <,opt_args>)

plot2d3 is the same as plot2d but curves are plotted using vertical bars. By default, successive plots are superposed. To clear the previous plot, use clf().

/ Define your independent values
x = [0 : 0.2 : 4*%pi];
/ your functions and plot.
/ The default color is black
plot2d3(x, sin(x))
/ 5 at the end means red line
plot2d3(x, sin(2*x), 5)
/ a red envelope on the red lines
plot2d(x, sin(2*x), 5)

vertical lines in Scilab plots - stems

Stems in Matlab



Stairs Function

Use plot2d2 for this purpose.

/ Define your variables and functions
t = linspace(-2*%pi, 2*%pi, 200);
r = sqrt( abs(2 * cos(4*t)) );
y = r .* cos(t);
/ Plot using a red line (5) and
/ bound axis from (-1.5, 0) to (1.6, 1.5)
plot2d2(t, y, 5, rect = [-1.5, 0, 1.6, 1.5]);
/ Add title, labels, legend and grid
title('Stairs/Steps Function');
xlabel('x'); ylabel('y');
legend('y = Step function');
xgrid;

Stairs in Scilab plots


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