Changing image in an algebraic loop

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Domi 2020-6-29

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https://ww2.mathworks.cn/matlabcentral/answers/556552-changing-image-in-an-algebraic-loop

编辑： Domi 2020-6-29

Hey guys,

I have a binary image which feeds a function in SIMULINK. The function changes parts of the binary image (a map) into free space (zeros) by writing it over with zeros. This runs in a algebraic loop with a delay block. So the output of the function, which is "newmap" gets back as "oldmap" into the function. I did the loop such that this changes permanently stay on the image. You can imagine an areay which of the image which was white (1) is now black (0).

small part of the code:

function newmap = fcn(map, cond, oldmap)
newmap = map;
if (cond ~= 0)     
    oldmap( ceil(abs(uRobot-(coneU*(1/12)))) :floor((uRobot+(coneU*(1/12)))), vRobot:floor((vRobot+sV)) ) = 0; 
    oldmap( ceil(abs(uRobot-(coneU*(2/12)))) :floor((uRobot+(coneU*(2/12)))), floor((vRobot+sV)):floor((vRobot+sV*2)) ) = 0; 
    oldmap( ceil(abs(uRobot-(coneU*(3/12)))) :floor((uRobot+(coneU*(3/12)))), floor((vRobot+sV*2)):floor((vRobot+sV*3)) ) = 0;
    oldmap( ceil(abs(uRobot-(coneU*(4/12)))) :floor((uRobot+(coneU*(4/12)))), floor((vRobot+sV*3)):floor((vRobot+sV*4)) ) = 0;
    oldmap( ceil(abs(uRobot-(coneU*(5/12)))) :floor((uRobot+(coneU*(5/12)))), floor((vRobot+sV*4)):floor((vRobot+sV*5)) ) = 0;
    oldmap( ceil(abs(uRobot-(coneU*(6/12)))) :floor((uRobot+(coneU*(6/12)))), floor((vRobot+sV*5)):(cv1_p) ) = 0;
    newmap = oldmap;
end

So, while I unterstand that this is running in a constant loop I want that if something in the original image (input: map) changes, it should also effect the image based on the algebraic loop.

to specify the problem: there is this input called map (binary image) into the function as one can see from the picture or code. The if-statement overwrites specific areas on the map right? Ok, but when the input "map" changes over time, it does not effect the output. The output updmap/newmap goes straight into an image viewer block. So it takes it when the simulation starts and than ignores it.

I hope someone understands my problem

Thank you & best regards

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Domi 2020-6-29

There is this input called map into the function as one can see from the picture or code. The if-statement overwrites specific areas on the map right? Ok, but when the input map changes over time, it does not effect the output. So it takes it when the simulation starts and than ignores it.

Domi 2020-6-29

I need a way to have this changes by the if-statement to stay on the image. But when something changes on the starting input, it should consider it.

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Answer 1

Fangjun Jiang 2020-6-29

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https://ww2.mathworks.cn/matlabcentral/answers/556552-changing-image-in-an-algebraic-loop#answer_458599

A better way in this case is to use persistent variable. doc persistent

But a loop with memory or delay block should also work. What is inside your "algebraic loop" subsystem. I think you need to debug your model first. Put an image viewer block on map to make sure input is changing first.

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Domi 2020-6-29

编辑：Domi 2020-6-29

I read the doc about persistent a couple days before and could not figure out how to implement it. That's why I tried it with the algebraic loop.

I try to describe my model in a better way:

The input map is an image which is generated by a usb camera and goes through filtering such that it becomes a binary image which is black and white (pic below). The variables cone and uRobot/vRobot are coordinates which change over time (based on a moving object). This coordinates create a specific shape on the map which is based on zeros. Thats why I did it like oldmap(val1, val2) = 0 etc. To make this changes from the if statement somehow permanent, it gets feeded back as an algebraic loop (subsystem with delay block).

The "cone" creates a cone-like shape onto the map/image and overwrites this area (based on the coordinates) with 0. The if statement is running in an infinty loop as it seems. Which means it does not consider the first input "map" at all.

Now, lets say while the simulation runs, the lower part of the image changes to full black bc the if statement is true. Now I put something into the image top corner. It is displayed on the map.. but it is not in the output of the function. It takes just a first snap out of map and uses it to overwrite everything. But when changes occure to the original input, nothing happens..

Fangjun Jiang 2020-6-29

You need to be more precise and accurate. "If statement" won't run in an infinity loop.

The MATLAB Function block is executed at every simulation step. If (cond ~= 0) is always satisfied, then nothing is wrong here. You need to look outside of this block to see when and how "cond" is affected by the output of "newmap". Otherwise, if the value of "cond" never changes, then the "if statement" is always executed in every simulation step. That is probably what you mean "infinity loop".

Domi 2020-6-29

编辑：Domi 2020-6-29

Oh yes. Sorry! That what I meant with infinite loop. The condition never changes, s.t. the if-statement runs in ervery simulation step.

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Changing image in an algebraic loop

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