can anybody tell me the meaning of "end-1" instruction here?thank you.

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lotus 2013-4-15

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                                                                                             ptot=15:1024;
sfdr=max(ptot(nper+2:end-1))

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Image Analyst 2013-4-15

"end" means the last element in the array, so "end-1" is the next to the last element in the array.

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Tobias 2013-4-15

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编辑：Tobias 2013-4-15

Not knowing what "nper" is makes it a bit more complex to explain, however, sfdr is set to be equal the max value of ptot in the interval going between nper+2 and the 2nd to last value (end-1)

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Tobias 2013-4-15

在 MATLAB Online 中打开

No, the max value in this case would be 1023.

>> ptot = 15:1024;
>> nper = 15;
>> sfdr=max(ptot(nper+2:end-1))
sfdr =
          1023

And for (end-2)

sfdr=max(ptot(nper+2:end-2))
sfdr = 1022

And so forth. Do you understand the notation (nper+2:end-1) ? In MATLAB you can process parts of your data, which is denoted as:

variable(rows,columns) or variable(start_value:end_value).

In your case you are telling MATLAB to find the max value in ptot(17:1023). As ptot is simply a count from 15 to 1024, your max value will always be the last one you include in your calculation interval.

lotus 2013-4-15