subscript indices must either be real positive integers or logicals - how to change lat/lons from double to integers?

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Madeleine P. 2012-5-16

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采纳的回答： Geoff

Hi,

I am executing a script for a global grid, using for i=1:144 for j=1:91 [z]=SPI ...etc end end

But I get the error message: subscript indices must either be real positive integers or logicals

The lat and lons were originally 'double' format in the source netcdf file... is there an easy way to change them to integers in matlab?

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Geoff 2012-5-16

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If they just need to be indices, you can use ceil, floor, fix or round. eg

x = fix(x)

If you want to convert them to ACTUAL integer types, you can use:

x = uint32(x);

[EDIT] As the question changes...

As Walter pointed out, you are overwriting Z every loop. Perhaps you wanted Z indexed by i and j... In which case:

Z(i,j) = SPI(precip30y_model1(i,j),12,12);

But since you said that Z is empty after iteration, is it possible that SPI() can return an empty set instead of a scalar? In that case:

Z = nan(144,91);
for i=1:size(Z,1)
  for j=1:size(Z,2)
    s = SPI(precip30y_model1(i,j),12,12);
    if ~isempty(s)
      Z(i,j) = s;
    end
  end
end

That uses NaN to represent "no data".

[EDIT 2012-05-23]

Okay, from your comments I think you want this:

Z = nan(144,91);
for i=1:size(Z,1)
  for j=1:size(Z,2)
    Z(i,j) = SPI(squeeze(precip30y_model1(i,j,:)),12,12);
  end
end

I think I know what's wrong, but don't know how to fix: my input dataset is 3 dimensions of rainfall, time (360), lat (91), lon(144) --> when ncread into matlab it gets transformed into lon,lat,time. This is monthly data which gets is supposed to be transformed into 1 output variable (SPI) per gridcell (i,j,) (via the gamfit and gamcdf matlab functions). So I am currently using 3 'for loops' i.e. i=144, j=91 and k=360, (without the k for loop, I get an error message 'subscripted assignment dimension mismatch', but Z cannot be calculated every month - it needs years of data (at least 30) to calculate 1 value of SPI, so if I have the time loop getting the script to try to calculate SPI every month, it's not going to work... this is why the script says the data should be month data vector not matrix (monthly or seasonal precipitation).

How to fix this, given that my input data is in 3 dimensions -I cannot use the time for loop, but get the above error message when I do... ?

Madeleine P. 2012-5-24

Ok, some progress has been made, at least in understanding of what I want to calculate. I do actually calculate a value of Z for each lon,lat,time values. So Z - which is a function, should actually be 3 dimensional. So I ran your code above (2012-05-23) for 3 dimensions (and no squeeze) and I got the error message 'subscript indices must either be real positive integers or logicals.

My code was:

Z = nan(144,91);

for i=1:size(Z,1)

for j=1:size(Z,2)

for k=1:size(Z,3)

Z(i,j,k) = SPI(precip30y_model1(:,:,:)),12,12);

end

When I tried the same thing with just [Z] = SPI(precip30y_model1(:,:,:)),12,12); ... I get the error message 'colon operands must be real scalars, yet when I use the [Z] = SPI(precip30y_model1(i,j,k)),12,12); I get an empty array [Z] for my troubles, as we've already covered previously.

And yet, when I run the script for 1 gridpoint:

[Z] = SPI(precip30y_model1(116,87,:)),12,12);

I get an array of [Z] = 1x348 (which is now what I realise I should get) -and the values all look right (and 348 is ok too as the script discards the first lot of months according to the scale (i.e. in this case 12). So the script works for 1 point but I just can't get it to work for the entire globe.

If I create the NaN array, then use the 3 loops for lon, lat, time, then [Z]=SPI(precip(144,91,360),12,12); I get a blank array really quickly (i.e. Z is not array, and yet I have never made [Z(i,j,k)] work.

So at this point, I'm at a loss. I hear NCL are bringing out their own function for SPI sometime this month - maybe I'll have better luck with it.

Anyway, thanks for your help- I really appreciate it. However I think that this function was not designed to be looped over a lat/lon grid....

Madeleine P. 2012-5-24

Hi, this seemed to work, in that I have an array of Z(348,144,91), and when I try to look at the data max(Z) and min(Z) I get reasonable answers. (and not nans). Is there like an ncdump command for matlab which will let me look at all the data stored in Z? Unless I can do this i won't know if I am calculating exactly what I want. I have tried to write it to a netcdf file so I can export it and work with it in a language I'm actually familiar with (i.e. NCL), but am having trouble; I'm trying:

> nccreate('spi_model1.nc','spi');

>ncwrite('spi_model1.nc','spi',Z);

But am getting an error message 'number of input elements does not match variable size'.

I tried the harder way:

spi=Z(360,144,91);

ncid=netcdf.create('spi_model1.nc','NOCLOBBER');

dimid=netcdf.defDim(ncid,'time',348);

dimid=netcdf.defDim(ncid,'lon',144);

dimid=netcdf.defDim(ncid,'lat',91);

varid=netcdf.defVar(ncid,'spi','NC_DOUBLE',dimid);

netcdf.putVar(ncid,varid,spi);

netcdf.close(ncid);

---this got me the same error message! And yet, in my workspace window, it's telling me I have a variable Z(348,144,91) ? It would seem like the variable Z may not contain what it's supposed to contain; I need to look at all the data -how do I do this?

Walter Roberson 2012-5-24

nccreate() creates a scalar variable unless you specify dimension information.

To fix the other problem:

dimid(1) = netcdf.defDim(ncid,'time',348);

dimid(2) = netcdf.defDim(ncid,'lon',144);

dimid(3) = netcdf.defDim(ncid,'lat',91);

Madeleine P. 2012-5-26

Walter Roberson, your experiment seems to have worked! I'm now outputting netcdf files with spi. Thanks so much to you and Geoff for your suggestions and persistence in helping me! (even when I was about to give up). Cheers, M.P.

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