do loop only running once
I am writing a program to solve a quadratic function iteratively by having values of x converge, with the program solving for x until the difference between the new value of x and the old value of x is less then 0.0001. My do loop is only executing once and I cannot figure out why.
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Hmm ...
I can't think of any numbers which are both positive and a little bit larger than zero and also are negative and a little bit less than zero, all at the same time.
You might find
http://www.cplusplus.com/reference/cmath/abs/
while(difference > 0.0001 && difference < -0.0001);I can't think of any numbers which are both positive and a little bit larger than zero and also are negative and a little bit less than zero, all at the same time.
You might find
abs(difference) useful.http://www.cplusplus.com/reference/cmath/abs/
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In line 28, do you mean the opposite, i.e.
while(difference <= 0.0001 && difference > -0.0001);
while(difference <= 0.0001 && difference > -0.0001);
I changed line 28 (revised code below), but the loop is still only running once.
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What's the point of the second comparison?
abs() will always return a positive number which will be covered by the first test. Comparing a positive number > a negative number will always be true.
abs() will always return a positive number which will be covered by the first test. Comparing a positive number > a negative number will always be true.
You've combined 2 positives to make a negative. Why compare against negative values after fetching the absolute value?
abs(x) will always give you a positive value or 0.
abs(difference) will therefore always be greater than -0.0001
You want something like while (abs(difference) < 0.0001)
Unfortunately, you're still in trouble, because abs() expects and returns int, so your doubles will all be truncated and you end up comparing a bunch of zeros.
If you want to loop UNTIL the difference falss in the range -0.0001 t0 +0.0001, try:
while(difference > 0.0001 || difference < -0.0001);
However, looking at your code, you're headed for an infinite loop, since you don't change x in the loop. You'll just get the same results over and over again.
abs(x) will always give you a positive value or 0.
abs(difference) will therefore always be greater than -0.0001
You want something like while (abs(difference) < 0.0001)
Unfortunately, you're still in trouble, because abs() expects and returns int, so your doubles will all be truncated and you end up comparing a bunch of zeros.
If you want to loop UNTIL the difference falss in the range -0.0001 t0 +0.0001, try:
while(difference > 0.0001 || difference < -0.0001);
However, looking at your code, you're headed for an infinite loop, since you don't change x in the loop. You'll just get the same results over and over again.
or do this:
The calculations look a bit suspect. The values of a, b and c are not used.
What I would expect to see is the evaluation of f(x) and f'(x). the next value of x is then calculated as x - f(x) / f'(x)
See for example: http://www.analyzemath.com/calculus/applications/newtons_method.html
difference = abs(x - Xnew); and while (difference > 0.00001); The calculations look a bit suspect. The values of a, b and c are not used.
What I would expect to see is the evaluation of f(x) and f'(x). the next value of x is then calculated as x - f(x) / f'(x)
See for example: http://www.analyzemath.com/calculus/applications/newtons_method.html
I revised the program code again, actually using a, b, and c this time, and fixing the loop, but after I enter the a, b, and c, I'm getting this:
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In one way that looks like progress, it is actually looping. But the calculation and testing of
I'm not sure what formula is being used in the calculation:
it doesn't look at all like the Newton-Raphson method.
Which algorithm are you using to derive
difference will need to use abs() - at least if you want to keep things simple.I'm not sure what formula is being used in the calculation:
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Which algorithm are you using to derive
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