Why function crashes when using conditional statements?

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Tara Behmanesh 2020-7-2

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评论： Geoff Hayes 2020-7-5

Hi In function "chapter" there is a statement that for some reason denominator of a fraction in that statement my be zero. So I need to check and see if it is less than a particular amount (for example 0.1) I should replace the denominator with 1 . But when i tried if-else and switch-case and both of them caused crash. Hope you can help me :) Sorry for my bad English.

Matlab R2018a

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Answer 1

Geoff Hayes 2020-7-2

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Tara - try replacing the switch with an if and use a tolerance check (note that using a switch statement for doubles or floats will not work as expected because of how floating point numbers are represented - see Floating-Point Numbers for more details)

pa=2*0.11*(1-(F(3)-Fa0)/Fa0);
pc=2*0.11*(F(3)-Fa0)/Fa0;
% the amount of pc should be checked .if pc is less than eps it should be
% replaced with "1"  in ''sqrt(pa/pc)'' term.
if abs(pc) < eps
    ra=-k.*sqrt(pa).*(pa-(pc/kp.*pa).^2);
else
    ra=-k.*sqrt(pa/pc).*(pa-(pc/kp.*pa).^2);
end 

Note tha I changed the above code to use eps instead of 0.1 which may or may not be appropriate for your code.

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Tara Behmanesh 2020-7-4

编辑：Tara Behmanesh 2020-7-4

Hi again I ran my function and let it be for some minutes and then I paused it I think the problem is in this line but I have no idea what it is about? Can you guide me?

In ode45.m Line 344

      err=absh*norm((fE)) ./ max(max(abs(y),abs(ynew)),threshold),inf);
    if nonNegative && (err <= rtol) && any(ynew(idxNonNegative)<0)

I understand that in code above there are many variables that I didn't mention the definition but I was wondering maybe you know what is that if statement about? (What it checks?) Really appreciated

Geoff Hayes 2020-7-5

Tara - that code is part of the ode45 function from MATLAB which would have been executing when you paused the program. I don't think that there is any reason to believe that there something incorrect about this line. I still think that you need to review your chapter code.

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