How can I make a flat,horizontal line appear in Matlab when my values are less than zero?

Question

Ruten9 2015-10-25

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/250952-how-can-i-make-a-flat-horizontal-line-appear-in-matlab-when-my-values-are-less-than-zero

评论： Image Analyst 2015-10-26

clear all; clc;
t = 0:.01:35;
h = height(t)
%Part C (maxima)---I swapped the order for the plotting
%max function
[xpsudeomax,ymax] = max(h(t));   
xrealmax = t(ymax);
maxfunction = [xrealmax,ymax];
%fminbnd function
[xmax2,ymaxpsudeo]= fminbnd(@(t) (-1.*h(t)),0,30);
yrealmax = -1.*ymaxpsudeo;
format long g
fminbndmax = [xmax2,yrealmax] ;
%Part D --- awkward position was for plotting
[xzero,ypsuedozero]= fzero(@(t) h(t),20);
yrealzero = round(ypsuedozero);
ZERO = [xzero,yrealzero];
%Part B (height vs time) 
figure;
plot(t,h(t),'blue',xmax2,yrealmax,'go','LineWidth',2);
hold on;
plot(xzero,yrealzero,'r.','MarkerSize',20);
ylabel('altitude [m]');
xlabel('time [sec]');
title('Rocket Trajectory');
legend('height','max','ground','location','ne')
axis([0 35 0 1500]);

If you load this, you'll get a graph that stops at the red dot. I want a blue line to appear on the x-axis after it touches the red dot. How can I do this?

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Image Analyst 2015-10-25

It doesn't run because you did not include the "height()" function.

Ruten9 2015-10-25

编辑：Walter Roberson 2015-10-26

在 MATLAB Online 中打开

function h = height(t)
h(:,1) = @(t) ((-9.8).*(2.^(-1))).*(t (:) .^2) + 125.*t(:) + 500;
%h(h<0) = 0;
if h(t) <0
    h=0
end
 end

This is my height.m file . The commented section keeps giving me an error.

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Answer 1

Thorsten 2015-10-26

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/250952-how-can-i-make-a-flat-horizontal-line-appear-in-matlab-when-my-values-are-less-than-zero#answer_197346

在 MATLAB Online 中打开

function h = height(t)
h = ((-9.8).*(2.^(-1))).*(t (:) .^2) + 125.*t(:) + 500;
h(h<0) = 0;
end

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Answer 2

Image Analyst 2015-10-25

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/250952-how-can-i-make-a-flat-horizontal-line-appear-in-matlab-when-my-values-are-less-than-zero#answer_197297

在 MATLAB Online 中打开

This is what I used:

function test3
clc;    % Clear the command window.
t = 0:.01:35;
h = height(t)
%Part C (maxima)---I swapped the order for the plotting
%max function
[xpsudeomax,ymax] = max(h(t));
xrealmax = t(ymax);
maxfunction = [xrealmax,ymax];
%fminbnd function
[xmax2,ymaxpsudeo]= fminbnd(@(t) (-1.*h(t)),0,30);
yrealmax = -1.*ymaxpsudeo;
format long g
fminbndmax = [xmax2,yrealmax] ;
%Part D --- awkward position was for plotting
[xzero,ypsuedozero]= fzero(@(t) h(t),20);
yrealzero = round(ypsuedozero);
ZERO = [xzero,yrealzero];
%Part B (height vs time)
figure;
plot(t,h(t),'blue',xmax2,yrealmax,'go','LineWidth',2);
hold on;
plot(xzero,yrealzero,'r.','MarkerSize',20);
ylabel('altitude [m]');
xlabel('time [sec]');
title('Rocket Trajectory');
legend('height','max','ground','location','ne')
axis([0 35 0 1500]);
function h = height(t)
h(:,1) = @(t) ((-9.8).*(2.^(-1))).*(t (:) .^2) + 125.*t(:) + 500;
%h(h<0) = 0; if h(t) <0 h=0 end end

and this is what it produces:

Then you say "you'll get a graph that stops at the red dot. I want a blue line to appear on the x-axis after it touches the red dot"

I'm not sure exactly what that means. What I would suggest you try is to either plot a red circle instead of a dot using 'ro' or plot the blue line after you plot the red dot/circle.