Using quiver to vary magnitudes of the vector

Hi there,

I need to change the magnitude of each point on a quiver plot. Here is the code;

py= 49.35/Dmm;
px = (0.3125*Dmm)/Dmm;
g = streamline(X,Y,vx,vy,px,py); %plotting the upper line
x = g.XData;
y = g.YData;
xx = x(ind);
yy = y(ind);
dx = gradient(xx)
dy = gradient(yy)

[dx,dy] = magvec(9, dx ,dy)  %Custom function to change magnitude
p = plot(xx,yy,'r') %stream line 
f = quiver(xx,yy,-dy,dx,'g') % plotting the components

the -dy, dx is to plot the vectors outward to the line. i'm not sure how quiver works, but the problem is that the result plotted isn't tangent to the stream line after i pass the dx and dy values through the magvec function, but is tangent and works correctly when i dont pass it through the magvec function. The error could be in magvec, and there are some redundancies in the function (could have multiplied dx by mag directly), but otherwise nothing (that i can see) should cause an error.

i'd really appreciate any help here.

this figure shows the plot after using magnitude as 2 for the upper contour, which should ideally be larger than the lower one.

the function that i used to change the magnitude:-

function [x,y] = magvec(mag, dx ,dy)

    oldmag = (dx.^2+dy.^2).^0.5;
    newmag = oldmag.*mag;
    ratio = newmag/oldmag;
    x = dx.*ratio;
    y = dy.*ratio;
end

[darova]

Here is the problem

But there is no need in such operations. YOu are calculating ratio

ratio = oldmag.*mag./oldmag;
ratio = mag;

Answer 1

[darova]

• but the problem is that the result plotted isn't tangent to the stream

Why did you change dy and dx order here?

f = quiver(xx,yy,-dy,dx,'g') % plotting the components

[yashvini shukla]

coz i needed to plot normal -- y= mx +c, and normal is n = -1/m

[darova]

Maybe problem is in quiver scaling

what about this

f = quiver(xx,yy,-dy,dx,'g',4) % plotting the components

[yashvini shukla]

i tried that, its not working...