# If statement dictating acceptable range is not functioning properly, why?

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Aly Osman el 10 de Jun. de 2022
Comentada: Aly Osman el 10 de Jun. de 2022
I'm working on a project to where I have to find pairs of values that provide the same output when inputted into an equation. I want only combinations that provide an output within a defined range, so for example, say I want all the possible combinations of values that sum to 6 +/- 0.5 so combinations that would sum to 5.5, 6 or 6.5 are all acceptable, however if there's a combination that sums to 7, I want that to be excluded. Getting a code working that at least satisfies the process of finding combinations is something I already have, thanks to the gracious people on here in this thread , so my issue is setting the condtions that I just spoke of to exclude certain combinations.
In my test code however, it doesn't seem like this is being done for some reason. I want all combinations that give me a value that is between lim1 and lim2, however when plugging the combinations that are output back into the original equation to find davg, I find that it has cominations that output values way beyond the conditions that I set (for example davg(1)= 89.3, when I set a condition for no combinations that would result in davg being greater than 59.663). So is something off with my if statement, or am I off base here completely? I would appreciate some insight regarding this.
lim1=(davg_initial-0.5);
lim2= (davg_initial+0.5);
a = [0:0.5:35];
n = length(a);
b = [];
for i = 1:n
value1 = a(i);
for j = 1:n
value2 = a(j);
if davg<=lim2 && davg>=lim1...
&& value2<value1
b = [b,[value1;value2]];
end
end
end
b'
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Steven Lord el 10 de Jun. de 2022
Just a suggestion: rather than repeatedly converting back and forth between degrees and radians I recommend using the degree-based trig functions. Here's a simple example:
format longg
s = sind(35);
ans = 2×1
0.573576436351046 0.573576436351046
c = cosd(35);
[c; c2]
ans = 2×1
0.819152044288992 0.819152044288992
ct = cotd(35);
[ct; ct2]
ans = 2×1
1.42814800674211 1.42814800674211
% Check: cot(x) = cos(x)/sin(x)
check = [ct; c./s]
check = 2×1
1.42814800674211 1.42814800674211
Aly Osman el 10 de Jun. de 2022
Good suggestion! I've used cosd, sind in the past, but for some reason my mind blanked on using them here since originally I was doing everything in radians and to understand what each number meant I was just doing rad2deg, regardless, I'll switch to this now, much cleaner and shorter! Thank you!

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Geoff Hayes el 10 de Jun. de 2022
@Aly Osman - what are the units for a and so the units for b? In your looping code, that includes the if statement, you do
for i = 1:n
value1 = a(i);
for j = 1:n
value2 = a(j);
if davg<=lim2 && davg>=lim1...
&& value2<value1
b = [b,[value1;value2]];
end
end
end
where you take pairs of values from a and pass them into the equation
If the criteria is met, then you save value1 and value2 to the b array. Once the outer loop completes, then you seem to do a check or validation of the data
where you convert each value in b from degrees to radians, and then you pass them into the (almost identical) equation
So why is there a conversion from degress to radians of the data in b? Shouldn't you have done that also when extracting value1 and value2 from a?
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Aly Osman el 10 de Jun. de 2022
Wow, I'm a dummy it seems. You are right, value 1 and value 2 are in radians instead of being in degrees, which is what messed everything up. This fixed it and now the numbers are actually within the range I designated in the if statement. Thank you!

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