Detrending relative strengh index

Greetings,

I have a question regarding a technical analysis indicator used for algorithmic trading. My question relates to the following Matlab Demo: https://www.mathworks.com/matlabcentral/mlc-downloads/downloads/submissions/29489/versions/3/previews/AlgoTrading2010/html/AlgoTradingDemo2.html

In this Demo the author uses the relative strength index by using the function rsindex(). Normally this index is used on closingprices of an asset. The author however suggests to detrend the closing prices by substracting a moving average and calculating the relative strengh index on this detrended time series. This should improve the quality of signals generated from this indicator. His exact line of code is:

rsindex(BundClose-movavg(BundClose,30,30),14); where BundClose is a timeseries of closing prices.

However, when I run this line of code on my own price data, I get this error message:

"Expected Closing Price to be nonnegative."

This makes sense, as the price will sometimes be below it's moving average. So I'm wondering why it worked in the demo mentioned and how best to go about calculating such a bounded indicator on detrended price series.

Thanks in advance!

[Javier Ossa]

movavg and rsindex in R2010, dont have the same syntax as in R2019 or R2020

rs2 = rsindex(BundClose-movavg(BundClose,30,30),14);

Ma = movavg(BundClose,'exponential',30)

rs2 = rsindex((BundClose-Ma),'WindowSize',14)

But still have same result!

"Expected Closing Price to be nonnegative."

[Javier Ossa]

this why is negative and Zero

%rs2 = rsindex(BundClose-movavg(BundClose,30,30),14);

BundClose

BundClose = 11339×1

106.61

106.57

106.53

106.48

106.47

106.42

106.5

106.47

106.47

106.47

movavg(BundClose,'exponential',30)

ans = 11339×1

106.61

106.607419354839

106.602424557752

106.594526199188

106.586492250853

106.575750815314

106.570863665939

106.564356332653

106.55826882732

106.552574064267

BundClose-movavg(BundClose,'exponential',30)

ans = 11339×1

0

-0.0374193548387183

-0.0724245577523561

-0.114526199187694

-0.116492250853014

-0.155750815314107

-0.0708636659390152

-0.0943563326526373

-0.0882688273202206

-0.0825740642673196

rs2 = rsindex((BundClose-movavg(BundClose,'exponential',30)),'WindowSize',14)

should i use absolut values from the ma?

[Javier Ossa]

I need to check the math formula from RSI