adding foci points to my hyperbola in Matlab

Posted on 2009-03-30
Last Modified: 2016-02-10
Please find the matlab code below;

ok... I figured out that my foci points : d=+/- sqrt(a) +sqrt(b)
Is this ok?

and how do I add this to my code below

thanks in advance
% Program to plot the hyperbola

% y^2/a^2 - x^2/b^2 = 1

% The hyperbolae are open up/down, so that x is the independent variable

% for plotting. (Using the form x^2/a^2 - y^2/b^2 = 1 requires that y be

% the independent variable, which is awkward programming-wise.)

clear % all variables

figure(1), hold off % start a new figure

set(gca,'FontSize',14) % adjust fontsize

xmax = 30; ymax = 20;

x = linspace(-xmax,xmax,1001); % array of x values for plot : This function generates vector with 1001 points equally distributed between -xmax and xmax. 

                                %1001 is probably to have 500 points on one side (>0), 500 on another side (<0) and to include 0 itself. So you will have 

                                 %more natural numbers. 

a = 5; b = 3;

y=sqrt(((x.^2)./(b^2)+1).*a^2); % corresponding y values


hold on % add to current plot

plot(x,-y) % Plot other half of hyperbola

axis([-xmax xmax -ymax ymax]) % specify axis limits



title(['Hyperbola $y^2/a^2 - x^2/b^2 = 1$; $a$ = ', num2str(a), ...

', $b$ = ', num2str(b),'; (WR 1/21/08)'],'Interpreter','latex')

% Add axes

plot([0 0],[-ymax ymax],'k') % y axis (black line - k)

plot([-xmax xmax],[0 0],'k') % x axis


% Program to plot the elipse

% y^2/a^2 - x^2/b^2 = 1


y=sqrt(((-x.^2)./(b^2)+1).*a^2); % corresponding y values


hold on % add to current plot

plot(x,-y) % Plot other half of elipse

axis([-xmax xmax -ymax ymax]) % specify axis limits



title(['Hyperbola and elipse $y^2/a^2 + x^2/b^2 = 1$;$y^2/a^2 - x^2/b^2 = 1$; $a$ = ', num2str(a), ...

', $b$ = ', num2str(b),';'],'Interpreter','latex')

% Add axes

plot([0 0],[-ymax ymax],'k') % y axis (black line - k)

plot([-xmax xmax],[0 0],'k') % x axis

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Question by:jtiernan2008
  • 3
LVL 15

Expert Comment

ID: 24023169
Are those points at x=0? Then you can add them with
plot([0 0], [-sqrt(a)+sqrt(b) sqrt(a)+sqrt(b)],'o')

Are you sure it's correct? May be this?
plot([0 0], [-sqrt(a^2+b^2) sqrt(a^2+b^2)],'ro')

Or this?
plot([0 0], [-a a],'go')

Please define what are foci points?


Author Comment

ID: 24023262

foci is focus plural

I actually done as follows.

text(0,f1,'\leftarrow +d')
text(0,f2,'\leftarrow -d')

Is this correct?
LVL 15

Accepted Solution

yuk99 earned 500 total points
ID: 24023521
If c^2=a^2+b^2, then c=+-sqrt(a^2+b^2). Is it focus points?

I'd also add VerticalAlignment and HorizontalAlignment to make sure the pointers positions are closest.



plot([0 0],[f1 f2],'.')

text(0,f1,'\leftarrow +d','VerticalAlignment','middle','HorizontalAlignment','left')

text(0,f2,'\leftarrow -d','VerticalAlignment','middle','HorizontalAlignment','left')

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LVL 15

Expert Comment

ID: 24023528
Or f2=-f1;

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