There is an apparent error in line 4, and this code only ran once

Question

Joshua Dominguez 2021-10-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1562896-there-is-an-apparent-error-in-line-4-and-this-code-only-ran-once

评论： Mathieu NOE 2021-10-13

Hello everyone, I am currently trying to figure out what is wrong with my code:

t = [36, 65, 100, 160];
c = [0.145, 0.120, 0.100, 0.080];
t2 = (20:10:160);
c2 = b*exp(t2*m);
plot(t, c)
plot(t, c, '*g', t2, c2, '-g');
P = polyfit(t, log(c), 1);
m = P(1);
b = exp(P(2));
TE = sprintf('C = %0.2fe^{%0.3ft}',b, m);
text(43, 0.085, TE);

I wrote 2 codes that are similar to the one above, but it said there is an error in line 4 (which matlab detected the same line for both codes) after I cleared everything in the command window. Is there an error that I am not aware of? Thanks

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Answer 1

Rik 2021-10-13

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https://ww2.mathworks.cn/matlabcentral/answers/1562896-there-is-an-apparent-error-in-line-4-and-this-code-only-ran-once#answer_807846

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t = [36, 65, 100, 160];
c = [0.145, 0.120, 0.100, 0.080];
t2 = (20:10:160);
c2 = b*exp(t2*m);
Unrecognized function or variable 'b'.

As you can see, you didn't define the variable b.

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Joshua Dominguez 2021-10-13

I just ran the code again, and I honestly forgot to run the code first before pluging in the codes for t2 and c2. thanks for your help

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Answer 2

Cris LaPierre 2021-10-13

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https://ww2.mathworks.cn/matlabcentral/answers/1562896-there-is-an-apparent-error-in-line-4-and-this-code-only-ran-once#answer_807851

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The issue I see is that you are using b in line 4 to calculate c2, but do not define b until line 9. Perhaps you just need to reorganize your code?

t = [36, 65, 100, 160];

c = [0.145, 0.120, 0.100, 0.080];

t2 = (20:10:160);

P = polyfit(t, log(c), 1);

m = P(1);

b = exp(P(2));

c2 = b*exp(t2*m);

plot(t, c, '*g', t2, c2, '-g');

TE = sprintf('C = %0.2fe^{%0.3ft}',b, m);

text(43, 0.085, TE);

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Mathieu NOE 2021-10-13

yeap

exactly what I already proposed

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Answer 3

Mathieu NOE 2021-10-13

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https://ww2.mathworks.cn/matlabcentral/answers/1562896-there-is-an-apparent-error-in-line-4-and-this-code-only-ran-once#answer_807856

在 MATLAB Online 中打开

hello

simply b and m are not yet defined when you do in line 4 :

c2 = b*exp(t2*m);

the code should be organized like this :

t = [36, 65, 100, 160];
c = [0.145, 0.120, 0.100, 0.080];
P = polyfit(t, log(c), 1);
m = P(1);
b = exp(P(2));
t2 = (20:10:160);
c2 = b*exp(t2*m);
plot(t, c, 'dr', t2, c2, '-b');
TE = sprintf('C = %0.2fe^{%0.3ft}',b, m);
text(t2(4), c2(4) + 0.004, TE);