How to find a value from column 1 for given column 2 and 3 values.

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Yahya Khan 2018-9-1

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https://ww2.mathworks.cn/matlabcentral/answers/417138-how-to-find-a-value-from-column-1-for-given-column-2-and-3-values

编辑： Matt J 2018-9-2

Hi there, new to Matlab and have a small task which I need help with.

I have three columns, first shows velocity, second shows x-coordinates and third shows y-coordinates. I want to be able to find the velocities for given x,y coordinates. I have about 36,000 values for each so basically need an efficient way to do this. Thanks in advance.

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madhan ravi 2018-9-1

can you upload the datas as a file by clicking the paper clip button.

Yahya Khan 2018-9-1

Symm_plane.csv

I need to be able to create a control volume, so basically a square that has velocity for each point along the boundary. The csv file has u-velocity, v-velocity, x-coordinate, y-coordinate and z-coordinate. I can basically ignore the z-coordinates and work with u an v velocities separately.

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Answer 1

Matt J 2018-9-1

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https://ww2.mathworks.cn/matlabcentral/answers/417138-how-to-find-a-value-from-column-1-for-given-column-2-and-3-values#answer_335038

在 MATLAB Online 中打开

Use griddedInterpolant

F=griddedInteprolant({x,y},velocity);

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Yahya Khan 2018-9-2

I've tried using griddedinterpolation but keep on getting errors such as 'grid vectors must be strictly monotonically increasing' What format do I need to have the data in? Also is it possible to create a matrix of velocity from the x,y coordinates as that would make it the most useful to work with?

Matt J 2018-9-2

编辑：Matt J 2018-9-2

There are several options for that which are explained in the griddedInterpolant documentation, but in this example, I intended x and y to be grid vectors.

Yes, you should give the velocity data to griddedInterpolant in matrix form, using reshape() appropriatately. If the velocity data is not sampled from a regular grid, you should probably be using scatteredInterpolant() instead.

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