How to interpolate these values?

2013 1 25
3 个回答
4 次查看（30 天）

0 个投票

Hi everyone. I have a table like this:
Well, I have to calculate for example the value for (ALFA = 14,2-CD=150) that there isn't in this table. I tried to calculate the equation in Excel with polynomial regression and also with INTERP in Matlab but it isn't accurate. I don't know where I am wrong. Can you help me? Thanks a lot.

3 个评论
显示 1更早的评论 隐藏 1更早的评论

Matt J
Matt J 2013-1-25
By the way, commas for decimals, e.g., ALFA = 14,2 are very prone to confusion in MATLAB forums since commas are used in MATLAB for other things.
Jan
Jan 2013-1-25
Please show us, how you use INTERP. Otherwise we cannot guess what's going wrong.
Giacomo
Giacomo 2013-1-25
I know. I'm sorry..

请先登录，再进行评论。

请先登录，再回答此问题。

回答（3 个）

Matt J
Matt J 2013-1-25

0 个投票

You should use INTERP2 or griddedInterpolant.

2 个评论
显示 无 隐藏 无

Giacomo
Giacomo 2013-1-25
Ok, let's try.
Matt J
Matt J 2013-1-25
编辑：Matt J 2013-1-25
Glad it worked. You may not be aware of the practice of Accepting answers. Please accept this one if it was what you needed.

请先登录，再进行评论。

Giacomo
Giacomo 2013-1-25
编辑：Giacomo 2013-1-25

0 个投票

Ok, I wrote:
load cl.txt
alfa=cl(2:61,1);
Reynolds=cl(1,2:8);
values=cl(2:61,2:8);
And if I ask
CL(150,14.2)= interp2(Reynolds,alfa,values,150,14.2)
it returns the right value. The new problem is that I have two matrices 17x11, Alpha and Re. Now, I have to calculate CL matrix (17x11) where (i,j) elements are calculated combined the (i,j) values of Alpha and Re through INTERP2 command.
Suggestions?
Giacomo
Giacomo 2013-1-25

0 个投票

I tried with:
for i=1:length(r)
for j=1:n+1
CL(i,j) = interp2(Reynolds,alfa,values,Re(i,j),alpha(i,j));
end
end
and seems work.
Thank you, Matt.

1 个评论
显示 -1更早的评论 隐藏 -1更早的评论

Matt J
Matt J 2013-1-25
You could also have done it with a single call to INTERP2 (which is faster) by doing
idx=sub2ind(size(Re),1:length(r),1:n+1);
CL(idx) = interp2(Reynolds,alfa,values,Re(idx),alpha(idx));

请先登录，再进行评论。

类别

在 帮助中心 和 File Exchange 中查找有关 Interpolation 的更多信息

标签

提问:

Giacomo
Giacomo
2013-1-25

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by