Interpolation Error using interp1

2015 4 28
2 个回答
回答已采纳
更新时间：2015 4 29
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0 个投票

I'm using a script to take these x and y values from a .txt file. At this point in the script the variables are assigned the fid is closed... When I code further, I'm trying to interpolate a user entered value which is called 'userx'.
Below, though, I am just trying to get it to interpolate at 100. I don't understand where my syntax error is.
>> x
x =
0
20
22
30
33
52
52
67
84
101
103
111
116
132
141
159
162
168
171
173
>> y
y =
8477
11886
11384
6087
7871
3003
1941
9213
10981
2179
2219
507
1593
8880
11650
4392
6118
4437
2094
1961
>> interp1(x,y,100) Error using interp1 (line 130) Values must be of type double or single.
>>

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 采纳的回答

Star Strider
Star Strider 2015-4-28

0 个投票

Check the data types of x and }y}. My guess is that they are either cells or strings.
If they are cells, you can convert them to double arrays with:
x = x{:};
y = y{:};

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Jorge Bastillo
Jorge Bastillo 2015-4-28
编辑：Jorge Bastillo 2015-4-28
I have a two columned .txt file, my script asks the user for the file name, checks available files, and locates it. The user input variable is fileput. I then assign the left column as x and the right column as y.
fid=fopen(fileput,'r');
data=textscan(fid,'%d %d','headerlines',1);
x=data{1};
y=data{2};
fclose(fid);
Now here in the command window I tried what you suggested... I think what you're saying is close to my problem.
>> x=x{:} Cell contents reference from a non-cell array object.
>> y=y{:}
Cell contents reference from a non-cell array object.
>> interp1(x,y,100)
Error using interp1 (line 130)
Values must be of type double or single.
>>
Not working though.
Star Strider
Star Strider 2015-4-28
The output of textscan is a cell array, so your code should be giving you a numeric array. My best guess is that there are more than one header lines, or other problems with the file.
I would have to have your file to experiment with to understand the problem.
Star Strider
Star Strider 2015-4-28
Jorge Bastillo’s ‘Answer’ moved here...
Also tried using cell2mat... Didn't work either.
>> a=cell2mat(x)
Cell contents reference from a non-cell array object.
Error in cell2mat (line 42)
cellclass = class(c{1});
Star Strider
Star Strider 2015-4-28
That would mean to me that your conversion from cell to numeric with:
x=data{1};
y=data{2};
was successful (and correct), and that the problems are with non-numeric entries in ‘x’ and ‘y’.

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更多回答（1 个）

Image Analyst
Image Analyst 2015-4-29

0 个投票

Try
x = double(x);
y = double(y);
to make sure they're doubles like interp1() said it wanted.

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