Finding x that approximate y to zero

2015 7 12
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更新时间：2015 7 12
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0 个投票

I am trying to find the the value x that make y approximately zero. Here is what I did:
e= 0.001 %error bar
for x = linspace(100, 170, 1000);
y = 18.9*log(x/170) +0.0042*(x-170) + 8.314*log(0.000267/0.0001413);
end
Thanks in advance.

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Azzi Abdelmalek
Azzi Abdelmalek 2015-7-12

0 个投票

e= 0.01 %error bar
x = linspace(100, 170, 1000);
y = 18.9*log(x/170) +0.0042*(x-170) + 8.314*log(0.000267/0.0001413);
idx=find(abs(y)<e)

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Abdullah Al-Alawi
Abdullah Al-Alawi 2015-7-12
Thank you for your quick response. That really helped me, but I want to know the value of X. like what value of x between this range( 100 to 170) that make Y approximately equal to zero. Thank you though for your time.
Azzi Abdelmalek
Azzi Abdelmalek 2015-7-12
If you are looking for the nearest value to 0.
e= 0.01 %error bar
x = linspace(100, 170, 1000);
y = 18.9*log(x/170) +0.0042*(x-170) + 8.314*log(0.000267/0.0001413);
[max_val,index_val]=min(abs(y))
Abdullah Al-Alawi
Abdullah Al-Alawi 2015-7-12
Thank you! Much Appreciated!

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更多回答（1 个）

Walter Roberson
Walter Roberson 2015-7-12

1 个投票

Consider
x0 = fzero( @(x) 18.9*log(x/170) +0.0042*(x-170) + 8.314*log(0.000267/0.0001413), [100, 170]);

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Abdullah Al-Alawi
Abdullah Al-Alawi 2015-7-12
Thank you Walter! That's indeed a faster way! Much Appreciated! You Rock!

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