A line at maximum value of y ?

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RS 2013-8-9

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https://ww2.mathworks.cn/matlabcentral/answers/84384-a-line-at-maximum-value-of-y

want to draw a line at maximum of yth value that will give at what value of x, y is maximum? that value I have to print with legend?

how can I plot perpendicular to this line and want to know value of x, mean at what value of x my y is max coming and i want value of x at which y is maximum and max(y)to be print in legend or somewhere in plot? How can I?

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Answer 1

Giorgos Papakonstantinou 2013-8-9

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/84384-a-line-at-maximum-value-of-y#answer_93961

在 MATLAB Online 中打开

line(get(gca,'Xlim'), [max(y) max(y)],'color', 'red')

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Giorgos Papakonstantinou 2013-8-9

编辑：Giorgos Papakonstantinou 2013-8-9

在 MATLAB Online 中打开

You need one line which is parallel to y axis:

line([x(xm) x(xm)],get(gca, 'Ylim'), 'color','r' )

This line is parallel to y axis at x0 which have ymax.

If I understand correctly you need also another line at x0 which you have ymax at a second curve: So that's a code what does what you want (plus the legend you asked for)

x=0:0.01:2*pi;
% Three curves
A=sin(x+2);
B=2*sin(x);
C=-(0.1-x).*(x-5);
% Plotting Three Curves
h=plot(x, A, x, B, x, C);
hold on
% Find the Ymax in each curve
ymaxA=max(A);
ymaxB=max(B);
ymaxC=max(C);
% Find the index of X which you have Ymax
xmaxA=find(A==max(A));
xmaxB=find(B==max(B));
xmaxC=find(C==max(C));
% Find X at Y=0
xA0=x(A==0);
xB0=x(B==0);
xC0=x(C==0);
% Plot a line for each curve PARALLEL to yaxis for each curve
limh=get(gca,'Ylim');
chrom=get(h,'color'); % find the color of each curve
line([x(xmaxA) x(xmaxA)], [limh(1) max(A)], 'color', chrom{1},'Linestyle',':')
line([x(xmaxB) x(xmaxB)], [limh(1) max(B)], 'color', chrom{2},'Linestyle',':')
line([x(xmaxC) x(xmaxC)], [limh(1) max(C)], 'color', chrom{3},'Linestyle',':')
% Add a legend
strA=sprintf(' x=%.1f at y=0\n x=%.1f at ymax', xA0, x(xmaxA));
strB=sprintf(' x=%.1f at y=0\n x=%.1f at ymax', xB0, x(xmaxB));
strC=sprintf(' x=%.1f at y=0\n x=%.1f at ymax', xC0(1), x(xmaxC));
legend(strA, strB, strC)

If you want to display the ymax instead of the string ymax then erase the word ymax from the strA etc. and add %.1f. Also you have to add at the end of the str's the max(A) etc.

If you want to restrict the range of the x axis

set(gca,'Xlim',[2 5])

Read about gca, line, find, legend and sprintf in the mathworks website! Read also about formatspec in sprintf.

RS 2013-8-10

编辑：RS 2013-8-10

在 MATLAB Online 中打开

ok its working; and when I am using subplot command error is something like that

b = subplot(2,1,2); plot(x1,y1(:,1:3)); xlabel('r)'); ylabel('s'); 
h=b;
limh=get(gca,'Ylim');
chrom=get(h,'color'); 
line([x1(xmaxA) x1(xmaxA)], [limh(1) max(y1(:,1))], 'color',   chrom{1},'Linestyle',':')
   Cell contents reference from a non-cell array object.

and after that I want to use combine both plot using

samexaxis('ab','xmt','on','ytac','join','yld',1);

So How can I overcome? At last also I want to put different scale on right y axis and upper x axis? How can I?

Giorgos Papakonstantinou 2013-8-10

编辑：Giorgos Papakonstantinou 2013-8-10

在 MATLAB Online 中打开

For the sameaxis I have no answer. I don't now what it does and who is the creator of it.

Give a new name to this (not to the subplot h=b):

nameplot=plot(x1,y1(:,1:3));

then

chrom=get(nameplot,'color');
line([x1(xmaxA) x1(xmaxA)], [limh(1) max(y1(:,1))], 'color',   chrom,'Linestyle',':'

If you only one plot then (i.e. after the subplot) then chrom is no longer a cell. So the indexing chrom{1} makes no sense. crom in this case is a vector with three elements.

If you want 2 y axis (one on the left and one the right) the use plotyy

And S it's better if you have another question to open another thread. Your first question has been fully covered. If you think that your question has been answered please accept it as answer.

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A line at maximum value of y ?

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