# Different colours for arrows in quiver plot

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Hamed Nobarani 2019 年 11 月 11 日

Hi Everyone,
I want to plot arrows with different magnitude and directions in different colors.The code need to calculate the angle of the each vector and fit them in the colormap.
This is what I have wrote but is there anyone that can help me to find the example or any other command or function in matlab that can plot this for me?
for i=1:40
structure(i,:,:)=rombohedral((i-1)*338+1:i*338,:);
X=structure(i,:,4);
Y=structure(i,:,5);
Z=structure(i,:,6);
U=structure(i,:,7);
V=structure(i,:,8);
W=structure(i,:,9);
C=zeros(338,3);
C(1:300,1)=1;
C(300:end,2)=1;
figure(i)
figure(i)
title('2D')
t=num2str(i);
xlabel([t,' ps'])
hold on
for j=1:338
if (U(j)>0)
quiver(X(j),Y(j),U(j),W(j),'color',[1 0 0])
elseif (U(j)<0)
quiver(X(j),Y(j),U(j),W(j),'color',[0 1 1])
elseif (V(j)>0)
quiver(X(j),Y(j),W(j),V(j),'color',[0 1 0])
elseif (V(j)<0)
quiver(X(j),Y(j),W(j),V(j),'color',[1 0 1])
end
end
end
##### 2 件のコメント表示非表示 1 件の古いコメント
Hamed Nobarani 2019 年 11 月 11 日
I want to use quiver which is corresponding to the magnitude and angle of the vectors and interpolate them in 360 degree colormap.

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### 採用された回答

Thorsten 2019 年 11 月 11 日
Create a circular colormap:
cmap = colormap(hsv(360));
In the loop: compute the angle and an index into the colormap from the angle
alpha = atan2(W(j), U(j)); % or V(j), W(j) depending on your elseif clause
Convert angle to index
if alpha < 1 % negative indices and 0 are invalid
idx = idx + 360;
end
set(h, 'Color', cmap(idx,:)) % before, change each quiver command to h = quiver(...)
##### 3 件のコメント表示非表示 2 件の古いコメント
Hamed Nobarani 2019 年 11 月 11 日
Thanks,
I have modified my code but I'm getting this error:
Index in position 1 is invalid. Array indices must be positive integers or logical values.
Error in Colormap (line 39)
set(h, 'Color', cmap(idx,:)) % before, change each quiver command to h = quiver(...)
for i=1:40
structure(i,:,:)=rombohedral((i-1)*338+1:i*338,:);
X=structure(i,:,4);
Y=structure(i,:,5);
Z=structure(i,:,6);
U=structure(i,:,7);
V=structure(i,:,8);
W=structure(i,:,9);
C=zeros(338,3);
C(1:300,1)=1;
C(300:end,2)=1;
figure(i)
figure(i)
title('2D')
t=num2str(i);
xlabel([t,' ps'])
hold on
for j=1:338
cmap = colormap(hsv(360));
alpha = atan2(V(j), U(j));
if alpha < 1
idx = idx + 360;
end
h=quiver(X(j),Y(j),U(j),V(j));
set(h, 'Color', cmap(idx,:))
end
end

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### その他の回答 (1 件)

Hamed Nobarani 2019 年 11 月 11 日
Hi
I have attached the example here:
clc
close all
clear all
deg=linspace(0,2*pi,720);
r=1;
hold on;
for i =1 :720
cmap = colormap(hsv(360));
u(i)=r*cos(deg(i));
v(i) = r*sin(deg(i));
alpha(i) = atan2(v(i), u(i));
if idx < 1
idx = idx + 360;
end
x(i)=0;
y(i)=0;
quiver(x(i),y(i),u(i),v(i),'color',cmap(idx,:))
axis equal
end

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