How to change a parameter during a plot?

Question

Eliot 2014-3-16

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https://ww2.mathworks.cn/matlabcentral/answers/121770-how-to-change-a-parameter-during-a-plot

编辑： Paul 2014-3-16

I would like to plot a function but change a value part way through the plot, specifically in the code below, for values of (x<M) I would like to set R = RL and for values of (x>M) I would like to set R = RR. Any help appreciated. Thanks

x = 0:0.01:2;
M = 1;
R = 2;
LR = 0.25;
RL = (0.5 / LR) * R;
RR = (0.5 / (1 - LR)) * R;
y = exp(-(4* * *R* * .^2*(log(2))*(M - x).^2)/(M.^2));
plot(x,y)
grid on

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Answer 1

Paul 2014-3-16

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/121770-how-to-change-a-parameter-during-a-plot#answer_128645

在 MATLAB Online 中打开

x = 0:0.01:2;
M = 1;
R = 2;
LR = 0.25;
RL = (0.5 / LR) * R;
RR = (0.5 / (1 - LR)) * R;
xL = x(x<M);
xR = x(x>=M);
y(x<M) = exp(-(4*RL.^2.*(log(2)).*(M - xL).^2)/(M.^2));
y(x>=M) = exp(-(4*RR.^2.*(log(2)).*(M - xR).^2)/(M.^2));
plot(x,y)
grid on

This is based logical indices, see: http://www.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html

I also removed all the * in your function, not sure if there are supposed to be constants there or something.

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Answer 2

Eliot 2014-3-16

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/121770-how-to-change-a-parameter-during-a-plot#answer_128682

Thank you very much for taking the time to answer, I understand how it works now, the bit I was missing was splitting the x array.

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Paul 2014-3-16

编辑：Paul 2014-3-16

在 MATLAB Online 中打开

There's also an easier method. You can make R a vector with the corresponding value for x<M and x>=M:

x = 0:0.01:2;
M = 1;
R = 2;
LR = 0.25;
RL = (0.5 / LR) * R;
RR = (0.5 / (1 - LR)) * R;
Rc(x<M) = RL;
Rc(x>=M) = RR;
y = exp(-(4.*Rc.^2.*(log(2)).*(M - x).^2)/(M.^2));
figure;
plot(x,y)
grid on