You could limit the values in your matrix to the first 4 decimal places but this is usually not a good idea unles there's a reasonable justification to do so. Take a look at the values you mentioned.
As you can see, limiting those values to the first 4 dp will not give you matching values.
Those same values in "short" format are
But the key point is that the format just affects what you see, not the actual values.
If you have principled reason to truncate the precision to 4 decimal places (ie, the instrument used to get the data is only precise to 3 dp), you could do so like this:
Trace_WcNew = round(Trace_Wc, 4);
Instead, if you're trying to find values in a row that are approximately equal to the max value of that row, use a threshold like this:
idx = abs(Trace_Wc(11,:) - max(Trace_Wc(11,:))) < 0.0001
This locates all values in row 11 that are within 0.0001 of the max. Here's what it's returns:
Columns 1 through 6
2.249999999999984 2.249999999999988 2.249999999999990 2.249999999999983 2.249999999999988 2.249999999999987
Columns 7 through 8
In that case, 0.0001 is somewhat arbitrarily chosen after looking at the data. Instead, you could use a threshold that is 1/10 of 1% of the range of your data such as
threshold = range(Trace_Wc(11,:))*.001