Could someone please optimize this code?

Question

The Merchant 2019-10-28

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/487815-could-someone-please-optimize-this-code

评论： Adam Danz 2019-12-15

My code:

v0 = 10
gamma = 0.1
for k=1:101
    theta = 0.8444 * pi/4 + (k-51)*0.0001;
    dt = 0.0000001;
    x = 0;
    y = 0;
    vx = v0 * cos(theta);
    vy = v0 * sin(theta);
    x = x + dt * vx;
    y = y + dt * vy;
    while (y>0)
        v = sqrt(vx*vx+vy*vy);
        vx = vx - dt * gamma * vx;
        vy = vy - dt * 9.81 - dt * gamma * vx;
        x = x + dt * vx;
        y = y + dt * vy;
    end;
    t(k) = theta
    a(k) = x
end;
plot(a)
[vv, jv] = max(a)
t(jv) / (pi/4)

2 个评论
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John D'Errico 2019-10-29

It can be terribly difficult to optimize code if we are not told what the code is supposed to do. A few words of explanation would be a great help there.

Adam Danz 2019-12-15

在 MATLAB Online 中打开

Original question by OP in case it is deleted (this user has deleted many questions after being answered).

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Could someone please optimize this code?

My code:

v0 = 10
gamma = 0.1
for k=1:101
    theta = 0.8444 * pi/4 + (k-51)*0.0001;
    dt = 0.0000001;
    x = 0;
    y = 0;
    vx = v0 * cos(theta);
    vy = v0 * sin(theta);
    x = x + dt * vx;
    y = y + dt * vy;
    while (y>0)
        v = sqrt(vx*vx+vy*vy);
        vx = vx - dt * gamma * vx;
        vy = vy - dt * 9.81 - dt * gamma * vx;
        x = x + dt * vx;
        y = y + dt * vy;
    end;
    t(k) = theta
    a(k) = x
end;
plot(a)
[vv, jv] = max(a)
t(jv) / (pi/4)

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Answer 1

Bob Thompson 2019-10-28

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/487815-could-someone-please-optimize-this-code#answer_398518

I don't know about 'optimized,' but I'm pretty sure you can remove the entire for loop by vectorizing. Also, suppressing your values will actually do a surprising amount to speed up run time. Anything visual takes a lot more time and power to output, even just numbers and letters.

v0 = 10;
gamma = 0.1;
range = (-50:50);
theta = 0.8444 * pi/4 + range.*0.0001;
dt = 0.0000001;
x = 0;
y = 0;
vx = v0 * cos(theta);
vy = v0 * sin(theta);
x = x + dt * vx;
y = y + dt * vy;
while y>0
    v = sqrt(vx*vx+vy*vy); % What does this do? It isn't used anywhere
    vx = vx - dt * gamma * vx;
    vy = vy - dt * 9.81 - dt * gamma * vx;
    x = x + dt * vx;
    y = y + dt * vy;
end
plot(x)
[vv, jv] = max(x);
t(jv) ./ (pi/4);

I suspect part of the problem is that your code doesn't ever actually produce a negative value for y. The first value is slightly >0, but after that all you're doing is adding more positive values.