plot limit problem for x sides

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amani
amani 2024-9-7
回答： nick 2024-9-12
the code show to me my plot just for x=12 i need it to work for x=0
i did the xlim and the ylim but i havn't no think !
semilogy(vec_SNR_dB,var_ber, 'c', 'MarkerSize', 3 );
ylim( [ 1e-6, 100 ] ); xlim( [ 0, 20 ] );
grid on;
hold on ;
can some one help me plz !
  2 个评论
Torsten
Torsten 2024-9-7
编辑：Torsten 2024-9-7
Maybe the first row or column of "vec_SNR_dB" starts with 0 and the second with 12. Or some elements are NaN so that they are not plotted. We can't tell without the data for "vec_SNR_dB" and "var_ber".
Tomasz
Tomasz 2024-9-9
编辑：Tomasz 2024-9-9
Ran in:
In the code you have
mod_order = 16;
vec_EbN0_dB = 0:2:20
vec_EbN0_dB = 1x11
0 2 4 6 8 10 12 14 16 18 20
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vec_SNR_dB = vec_EbN0_dB + 10*log10(mod_order)
vec_SNR_dB = 1x11
12.0412 14.0412 16.0412 18.0412 20.0412 22.0412 24.0412 26.0412 28.0412 30.0412 32.0412
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your problem is that you create the X vector for your plot using summation, and the second part of that sum is constant 12.0412 so your X vector will always start with an offset.
You must design vec_SNR_dB in a way that is tarts at 0.
Why not just use vec_EbN0_db? It starts at 0 and end at 20. And If you need somevery specific points on the X axis then just create a vecotr for those values manually, or figure out different formula.

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回答（1 个）

nick
nick 2024-9-12
Hi Amani,
It seems that the variable 'vec_SNR_dB', which represents the Signal to Noise Ratio in decibels, should be on the y-axis instead of the x-axis in the figure. The function 'semilogy' has arguments in the following order: (X,Y) where represents x- and y-coordinates respectively.
You can refer to the following documentation to learn more about the function 'semilogy':
https://www.mathworks.com/help/matlab/ref/semilogy.html
To represent the plot accurately, you should use the 'semilogy' function as follows:
semilogy(var_ber,vec_SNR_dB, 'c', 'MarkerSize', 3 );
Kindly please share a reproducible version of the code to narrow down the other potential problems.

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