How do I call elements to the same precision

I have a large matrix of values (> 1000x1000) and I wish to select elements of desired rows and columns and then calculate the sum of them to obtain a single value. The values in the matrix have a precision of 15 decimal places, however when I call and display them in the command window, they only have a precision of 4 decimal places. How do I call them and sum them to obtain a single value of the same precision (15 decimal places) please?

Code so far:- %%Matrix file name: Scan1_reconstruction.fits

>>a = Scan1_reconstruction(1:2, 4:5) %%this then only displays 4dp not desired 15dp >>sum(a) %%this then returns 2 values, not the desired total 1 value

Thanks

[Rik]

You're getting close to the precision a floating point value can provide, so it might be impossible.

Also, you are just looking at a display problem. You can display the number with fprintf('.15f',sum(partial_matrix(:))).

If you had gone to the trouble of reading the doc for sum, you would have noticed that sum operates on only one dimension of a matrix. With (:) you can force a matrix to a vector form, but this is not compatible with subindexing.

Answer 1

[Birdman]

The default display format is set to short, therefore you see 4 decimal places. If you want to see more, then type

format longg

and then display your variable again.