tline = fgetl(fid);
returns only the single line of data in the file as a character string; not any values represented by those numeric characters converted to numeric values. The expression
sub_chi=tline(10:20,11:12)
is a 2D indexing expression, hence the "out of bounds" error for the second expression which is interpreted as asking for lines 11 and 12 of a one-line expression.
To read these two values you need to use sscanf or textscan based on the format of the file but reading line-by-line and parsing those lines is the most difficult way to try to read a file...
Show a few lines of the file for guidance in needed, but consult
doc importdata
doc textscan
and other i/o functions to see which may fit your data file most closely. Or use the interactive import tool...
