how to use interp1() function

Question

zein 2020-2-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/505022-how-to-use-interp1-function

编辑： Stephen23 2020-2-12

采纳的回答： Stephen23

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I have tried to use interpt(1) function as i have time and pressure data.

the pressure data is highly scattered it look like that

firstly,I have used function : p0q=interp1(p0,tq) as show belows

_____________________________________________________________________________________

t1=t(x1:x2);
p01=p0(x1:x2);
tq=t(x1):0.000001:t(x2);
p0q=interp1(p0,tq);
figure 
plot (t1,p01,'o',tq,p0q,'*');
legend('p01','p0q');

_____________________________________________________________________________________

but the poq (interpolated result is empty) as shown in the figure

when i change it to

p0q=interp1(p0,tq,'pchip');

the interploted data are incorrect

is there something wrong in my code?or i am using the function incorrectly?

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KSSV 2020-2-12

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Answer 1

Stephen23 2020-2-12

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https://ww2.mathworks.cn/matlabcentral/answers/505022-how-to-use-interp1-function#answer_415165

编辑：Stephen23 2020-2-12

在 MATLAB Online 中打开

The problem is that you are using the default x values, which for a vector input are defined as

1:numel(v)

These default points only make sense if you are also requesting interpolation for x>=1 and x<=numel(v), but look at the x points you are requesting interpolation at: judging by your screenshot they are somewhere between 0.06162 and 0.06067. The points you are requesting lie nowhere close to the the input x values (for which you used the default values 1:numel(v), and which iare thus totally unsuitable for your task).

The solution is simple: you need to provide the input x values, i.e.:

p0q = interp1(t1, p0, tq);