I am trying to create a plot for certain values.

2017 3 5
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更新时间：2017 3 5
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I am trying to create a plot for certain values. I am having troubles defining my range as well as creating the correct plot. I am trying to create a for loop that goes through the loop with values theta 0 through 15. There is a value v_perp defined in the loop, and I want the plot to be of theta on the x axis and v_perp on the y. I only want it to plot values if v_perp is <= 0.4*v_tot. What I have so far is below:
v_min = 16.5;
v_avg = 18;
v_max = 19.5;
x_r = 21.45;
y_r = 1.265;
for theta = 0:15
A = -9.81/2;
B = (v_min*sin(30))+(v_min*cos(30)*tan(theta));
C = 1.265+21.45*(tan(theta));
y = [A B C];
t = roots(y);
v_perp = (-sin(-theta)*(16.5*cos(30)))+(cos(-theta)*((-9.81*t)+(16.5*cos(30))));
v_tot = sqrt((16.5*cos(30)).^2+(((-9.81*t)+(16.5*cos(30)))).^2);
end
%plot(theta,v_perp,'-r')
disp(theta) disp(t) disp(v_perp) disp(v_tot)

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回答（1 个）

Image Analyst
Image Analyst 2017-3-5

0 个投票

Try this:
v_min = 16.5;
v_avg = 18;
v_max = 19.5;
x_r = 21.45;
y_r = 1.265;
for theta = 0:15
A = -9.81/2;
B = (v_min*sind(30))+(v_min*cosd(30)*tand(theta));
C = 1.265+21.45*(tand(theta));
y = [A B C];
t = roots(y); % HAS 2 VALUES!!! Use the first one.
t_to_use = t(1);
v_perp(theta+1) = (-sind(-theta)*(16.5*cosd(30)))+(cosd(-theta)*((-9.81*t_to_use)+(16.5*cosd(30))));
v_tot = sqrt((16.5*cosd(30)).^2+(((-9.81*t_to_use)+(16.5*cosd(30)))).^2);
% Store whether this point is to be plotted.
if v_perp(theta+1) > v_tot
keepit(theta+1) = true;
else
keepit(theta+1) = false;
end
end
keepit
% Set rows not to keep to nan so they won't be plotted.
v_perp(~keepit) = nan;
theta = 0:15
plot(theta,v_perp, 'r-.', 'MarkerSize', 15)
but none of the v_perp values is ever greater than the v_Tot values. Also note I changed to the degree version of trig functions, like cosd() instead of cos(), and I'm using just one of the two t values.

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