Computation on arrays using loops

Question

Kacper Witasinski 2021-2-19

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https://ww2.mathworks.cn/matlabcentral/answers/750139-computation-on-arrays-using-loops

编辑： Kacper Witasinski 2021-2-23

Hello,

I want to create code that will do operations on specified values from the arrays. I have array X and array Y, where array Y is X-dependent. Array X looks more or less like this: [0 0 0 0 0 0 0 0 0 0 0 45.9 45.98 45.99 46 46 46 46 0 0 0 0 0 0 0 ...], it represents pulse-like behaviour. I want matlab to save in workspace the values of array Y that corresponds to the every last "0" of the array X before the pulse ''46'' happens on the length of the whole array.

I expect that for/while loop has to be applied, but I am not sure which one and how the statements should look like. I would appreciate any help. Thank You. I am using matlab2020b version.

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Answer 1

Stephen23 2021-2-19

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https://ww2.mathworks.cn/matlabcentral/answers/750139-computation-on-arrays-using-loops#answer_627779

在 MATLAB Online 中打开

Y = [2.659717,2.656496,2.656496,2.656173,2.662294,2.661328,2.660039,2.620416,2.614295,2.606242,2.600765,2.600443,2.590779,2.591745,2.590457,2.586913,2.58498,2.583048,2.585303,2.578216,2.577571,2.580793,2.57886,2.573061,2.575638]
Y = 1×25
    2.6597    2.6565    2.6565    2.6562    2.6623    2.6613    2.6600    2.6204    2.6143    2.6062    2.6008    2.6004    2.5908    2.5917    2.5905    2.5869    2.5850    2.5830    2.5853    2.5782    2.5776    2.5808    2.5789    2.5731    2.5756
X = [0,0,0,0,0,0,0,46.24,46.24,46.24,46.24,46.24,46,46,46,46,46,45.99,45.99,45.99,45.99,45.99,46,46,46,46,46,46,46,46,46,46,46]
X = 1×33
         0         0         0         0         0         0         0   46.2400   46.2400   46.2400   46.2400   46.2400   46.0000   46.0000   46.0000   46.0000   46.0000   45.9900   45.9900   45.9900   45.9900   45.9900   46.0000   46.0000   46.0000   46.0000   46.0000   46.0000   46.0000   46.0000
idx = diff(X~=0)>0;
out = Y(idx)
out = 2.6600

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Stephen23 2021-2-22

编辑：Stephen23 2021-2-22

在 MATLAB Online 中打开

out = Y([false,idx])
out = 2.6204

Kacper Witasinski 2021-2-23

编辑：Kacper Witasinski 2021-2-23

Works, but one note for people dealing with same problem in the future. Matlab returned an error "Dimensions of matrices being concatenated are not consistent." After I transposed idx everything works perfectly.

Regards and thank You once more Stephen.

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Answer 2

Steven Lord 2021-2-22

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https://ww2.mathworks.cn/matlabcentral/answers/750139-computation-on-arrays-using-loops#answer_630299

Since you seem to be describing change point detection, see the ischange function and/or the Find Change Points task in the Live Editor.

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Answer 3

KALYAN ACHARJYA 2021-2-19

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https://ww2.mathworks.cn/matlabcentral/answers/750139-computation-on-arrays-using-loops#answer_627744

编辑：KALYAN ACHARJYA 2021-2-19

在 MATLAB Online 中打开

"I want matlab to save in workspace the values of array Y that corresponds to the every last "0" of the array X before the pulse ''46'' happens on the length of the whole array."

Is this? Note for this problem loop can be avoided

idx=find(diff(X)==-46)+1

This idx gives the indices of x, where x equal to zero and it's corresponding previous data to be equal to 46

Afterwards

Y=X(idx)

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KALYAN ACHARJYA 2021-2-19

编辑：KALYAN ACHARJYA 2021-2-19

在 MATLAB Online 中打开

Yes as per my code gives transition indices (from 46 to 0 only)

Can you clarify again? In this X example, what would be the Y

X=[0 0 0 0 0 0 0 0 0 0 0 45.9 45.98 45.99 46 46 46 46 0 0 0 0 0 0 0 ]

Kacper Witasinski 2021-2-19

编辑：Kacper Witasinski 2021-2-19

The values of X array given by me are really exemplary values that should give general scope of the behaviour.

Corresponding values of Y are more or less constant (the difference is in third/fourth number after the decimal point) for zeros of X array. When the pulse happen, the values are decreasing in exponential way and then values are increasing in exponential way when pulse ends. I can show You how graphs looks like to give You the idea.

So I will write once again. For majority of time the values of array X are equal to 0. At some instant, there is a pulse and the values of array Y decrease. I need the exact values of array Y that corresponds to the last zero value of array X before the pulse happen for the whole length of array (Imagine that there are 10 pulses).

Small fragment of my data:

Y= [2,659717 2,656496 2,656496 2,656173 2,662294 2,661328 2,660039 2,620416 2,614295 2,606242 2,600765 2,600443 2,590779 2,591745 2,590457 2,586913 2,58498 2,583048 2,585303 2,578216 2,577571 2,580793 2,57886 2,573061 2,575638]

X=[0 0 0 0 0 0 0 46,24 46,24 46,24 46,24 46,24 46 46 46 46 46 45,99 45,99 45,99 45,99 45,99 46 46 46 46 46 46 46 46 46 46 46 and so on]

Please, dont mind comas.

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