How can I match a value on a matlab plot?

Question

Julia de Lange 2018-1-11

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/376722-how-can-i-match-a-value-on-a-matlab-plot

评论： Star Strider 2018-1-12

I have identified the first peak value in my dataset. I'd like to know the first x-value at the point at which this peak y-value occurs again. Any suggestions? p

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Star Strider 2018-1-11

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/376722-how-can-i-match-a-value-on-a-matlab-plot#answer_299714

编辑：Star Strider 2018-1-11

在 MATLAB Online 中打开

Use the ‘locs’ value:

[pks,locs] = findpeaks(Voltage, 'MinPeakDist',2000, 'NPeaks',1);
peakTimes = Time(locs);

See the plot call in my previous code to demonstrate how to do this.

EDIT —

‘I'd like to determine x (time) the next time 1.4147 (y, voltage) occurs.’

This will give all the ‘Voltage’ and ‘Time’ values that equal or exceed the initial peak value:

[D,S,R] = xlsread('Data.xls');
Time = D(:,1);
Voltage = D(:,2);
[pks,locs] = findpeaks(Voltage, 'MinPeakDist',2000, 'NPeaks',1, 'MinPeakHeight',1.2);
VoltageThreshold = Voltage - pks*0.99;
zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0);                    % Returns Approximate Zero-Crossing Indices Of Argument Vector
zx = zci(VoltageThreshold);
TimeNew = Time(zx);                                                     % Time Vector, Voltage >= VoltageThreshold
VoltageNew = Voltage(zx);                                               % Voltage Vector, Voltage >= VoltageThreshold
figure(1)
plot(Time, Voltage)
hold on
plot(Time(locs), Voltage(locs), '+g')
plot(TimeNew, VoltageNew, '+r')
hold off
grid

12 个评论
显示 10更早的评论隐藏 10更早的评论

Star Strider 2018-1-11

在 MATLAB Online 中打开

As always, my pleasure!

Do not edit the function. Define what ‘t1’ and ‘t2’ are, run the function on your entire data vector, and then edit the data.

Example —

[D,S,R] = xlsread('Data.xls');
Time = D(:,1);
Voltage = D(:,2);
[pks,locs] = findpeaks(Voltage, 'MinPeakDist',2000, 'NPeaks',1, 'MinPeakHeight',1.2);
VoltageThreshold = Voltage - pks*0.99;
zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0);                    % Returns Approximate Zero-Crossing Indices Of Argument Vector
zx = zci(VoltageThreshold);
TimeNew = Time(zx);                                                     % Time Vector, Voltage >= VoltageThreshold
VoltageNew = Voltage(zx);                                               % Voltage Vector, Voltage >= VoltageThreshold
t1 = 0.9;                                                               % Start Time 
t2 = 2.1;                                                               % End Time 
tlimidx = find((Time >= t1) & (Time <= t2));                            % Indices of ‘Time’ Between ‘1’ & ‘2’
TimeLimitIndices = zx((zx >= tlimidx(1)) & (zx <= tlimidx(end)));       % ‘zx’ Indices Meeting Criteria
figure(1)
plot(Time, Voltage)
hold on
plot(Time(locs), Voltage(locs), '+g')
plot(TimeNew, VoltageNew, '+r')
plot(Time(TimeLimitIndices), Voltage(TimeLimitIndices), 'ms')
hold off
grid

I use find and the index limit range here to define ‘TimeLimitIndices’. The ismember or intersect functions could also work. I did not experiment with them here.

Julia de Lange 2018-1-12

worked, thank you!

Star Strider 2018-1-12

As always, my pleasure!

请先登录，再进行评论。

Answer 2

SRT HellKitty 2018-1-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/376722-how-can-i-match-a-value-on-a-matlab-plot#answer_299709

在 MATLAB Online 中打开

Say you have data with peaks for the Y-Axis and linear data for the X-Axis

Y = [1:5,1:5,1:5];
X = [1:15];

Now you have 3 peaks in Y, when it equals 5. If you want to know what value of X is when Y is equal to 5 you could do a logical index;

X_at_peaks = X(Y == 5);

That would show that X is 5, 10, and 15 when Y is equal to 5.

2 个评论
显示无隐藏无

Julia de Lange 2018-1-11

编辑：Julia de Lange 2018-1-11

Let me give you more details. I have attached my data with one time (x) plotted versus voltage (y). I have found the first peak to occur at (1.037,1.4147). I'd like to determine x (time) the next time 1.4147 (y, voltage) occurs.

SRT HellKitty 2018-1-11