How can I apply the attached vector coding equation to a matrix in matlab?

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Kylie Davis
Kylie Davis 2016-5-25
评论： Star Strider 2016-5-27
I currently am using atan2d(y,x) but I am unsure whether that is accounting for the y(i+1)-y(i) and x(i+1)-x(i) nature of the equation. x and y are defined as the two matrices I am comparing (i.e. knee versus ankle joint angles during a gait cycle).

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Star Strider
Star Strider 2016-5-25
It won’t account for it unless you tell it to:
Theta_vc = atan2d(diff(theta1), diff(theta2));
NOTE — This should work with your data.
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Kylie Davis
Kylie Davis 2016-5-27
To be more specific... X is the ankle angle over a gait cycle, and y is the knee angle over a gait cycle. The vector coding phase angle I want is equal to tan-1(y(i+1)-y(i),x(i+1)-x(i)) for each consecutive data point (which is 101 points because data was normalized to 100% gait cycle).
Star Strider
Star Strider 2016-5-27
My code:
Theta_vc = atan2d(diff(theta1), diff(theta2));
does exactly what the expression in your image does. See the documentation on the diff function for details.
If you just have vectors, they will work with my code whether they’re row or column vectors. I don’t understand your gait cycle coding (an area peripheral to my areas of expertise). I would use atan2 or atan2d because they reflect the correct quadrants.
If you want to convert the angles you get as Theta_vc to 0°-360° or 0-2*pi, use the appropriate one of these functions:
Angles360 = @(a) rem(360+a, 360); % For ‘atan2d’
Angles2pi = @(a) rem(2*pi+a, 2*pi); % For ‘atan2’

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James Tursa
James Tursa 2016-5-25
编辑：James Tursa 2016-5-25
atan2d(y,x) will not do any difference calculations such as y(i+1)-y(i) or x(i+1)-x(i) as part of the calculation. So you would need to do that calculation before using atan2d (e.g. using the diff function). Are x and y 1D vectors or 2D matrices?
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Kylie Davis
Kylie Davis 2016-5-26
I believe it is 2D matrices. I am new to Matlab and am sorry if I'm asking a basic question. I appreciate your feedback thank you!

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