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

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Joshua Dominguez
Joshua Dominguez2021-10-13
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

回答(3 个)

Rik
Rik 2021-10-13
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.
  1 个评论
Joshua Dominguez
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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Cris LaPierre
Cris LaPierre 2021-10-13
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);

Mathieu NOE
Mathieu NOE 2021-10-13
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);

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