plotting a simple Graph

Hi everyone,

Trying to plot a graph unsucssesfully :((

alpha=2.2;
Mx0=34.8262;
My0=15.7563;
Mx=linspace(0,50,0.0001);

Interaction_Curve=(Mx./Mx0).^alpha+(My./My0).^alpha-1
plot(Interaction_Curve,Mx)

Thank You Very much

[madhan ravi]

You didn’t define My and you haven’t used the linspace() properly for Mx.

[Shimon Katzman]

So what is the correct way?

Answer 1

[Star Strider]

One problem is that ‘My’ is missing. Beyond that, the linspace arguments resulted in an empty vector for ‘Mx’.

It might be easier to plot this as an implicit function:

alpha=2.2;
Mx0=34.8262;
My0=15.7563;
Interaction_Function = @(Mx,My) (Mx./Mx0).^alpha+(My./My0).^alpha-1;
figure
fimplicit(Interaction_Function, [0 50  0 30])
ylim([0 30])

producing:

That seems to produce the sort of plot you want. Make appropriate changes to the second agrument in the fimplicit call to get the result you want.

[Shimon Katzman]

Hi Star,like always thank you so much.

The thing is that im using 2015a version and it errors me:

Undefined function or variable 'fimplicit'.

[Shimon Katzman]

i used

ezplot(Interaction_Function, [0 50  0 30])

and now it works well.

Thank you very much Star

[Star Strider]

My pleasure.

The contour function is another option.

Try this:

alpha=2.2;
Mx0=34.8262;
My0=15.7563;
Mx=linspace(0,50,25);
My=linspace(0,50,25);

[MX,MY] = meshgrid(Mx,My);
figure
contour(Interaction_Function(MX,MY), [0 0])

That should work. The contour function has been around as long as I can remember. It should allow the definition of the single contour at [0 0] in R2015a. (This imay be what the fimpllicit function does as well. It appears to produce the same plot.)

[Shimon Katzman]

Hi Star,

Small questions for you please,

1)how do i find the intersection point between those two graphs?

2)how do i change the color of one of the graphs?

Thank YOU

alpha=2.2;
Mx0=M_x;
My0=M_y;
Mx = linspace(0,50, 1000);
My = linspace(0,50, 1000); 
Interaction_Function = @(Mx,My) (Mx./Mx0).^alpha+(My./My0).^alpha-1;
figure
hold on
ezplot(Interaction_Function,[0 40  0 20])
MxdivMy = @(Mx,My) Mx-3*My;
ezplot(MxdivMy, [0 40  0 20])
grid on;

[Star Strider]

As always, my pleasure!

I do not have ‘M_x’ and ‘M_y’, so I cannot run your latest code.

[Shimon Katzman]

Oh, im sorry.. Mx0= 34.8262 My0= 15.7563

[Star Strider]

Not immediately obvious, so it took some time.

Try this:

alpha=2.2;
Mx0=34.8262;
My0=15.7563;
Mx=linspace(0,50,25);
My=linspace(0,50,25);

Interaction_Function = @(Mx,My) (Mx./Mx0).^alpha+(My./My0).^alpha-1;
MxdivMy = @(Mx,My) Mx-3*My;

[MX,MY] = meshgrid(Mx,My);
figure
hc1 = contour(Mx, My, Interaction_Function(MX,MY), [0 0])
hc2 = contour(Mx, My, MxdivMy(MX,MY), [0 0])

xy1 = hc1(:,2:end);                                             % ‘Interaction Function’
xy2 = fliplr(hc2(:,2:end));                                     % ‘MxdivMy’
[xy2u,ix] = unique(xy2(1,:), 'stable');                         % Unique ‘MxdivMy’
xy2i = interp1(xy2u(1,:), xy2(2,ix), xy1(1,:));                 % Interpolate To Same x-Coordinates
xy2i = [xy1(1,:); xy2i];
xint = interp1(xy1(2,:)-xy2i(2,:), xy1(1,:), 0);                % Interpolate To Find X-Intercept
yint = interp1(xy1(1,:), xy1(2,:), xint);                       % Interpolate To Find Y-Intercept

alpha=2.2;
% Mx0=M_x;
% My0=M_y;
Mx = linspace(0,50, 1000);
My = linspace(0,50, 1000); 
Interaction_Function = @(Mx,My) (Mx./Mx0).^alpha+(My./My0).^alpha-1;
figure
hold on
ez1 = ezplot(Interaction_Function,[0 40  0 20]);
MxdivMy = @(Mx,My) Mx-3*My;
ez2 = ezplot(MxdivMy, [0 40  0 20]);
plot(xint, yint, 'pr', 'MarkerSize',10, 'MarkerFaceColor','g')  % Plot Intercept
grid on;
hold off

That calculates and plots the intercept.

[Shimon Katzman]

Wow Star. Thank you so much!!

You Are The Best!

[Star Strider]

As always, my pleasure!

I very much appreciate your compliment!

Answer 2

[Image Analyst]

Try this:

alpha = 2.2;
Mx0 = 34.8262;
My0 = 15.7563;
Mx = linspace(0,50, 1000);
My = linspace(0,50, 1000);  % Not sure what My should be!!!
Interaction_Curve = (Mx./Mx0).^alpha+(My./My0).^alpha-1
plot(Mx, Interaction_Curve, 'b-', 'LineWidth', 2)
grid on;

Be sure to define My because I just guessed incorrectly.

[Shimon Katzman]

Hi, it doesnt plot the right graph :(

[Image Analyst]

I know. Because I don't have the value of the My variable. That's why I asked you to define it. What is it? But doesn't matter since it looks like Star figured it out.