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plotting three functions in the same graph with a specification

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Noi Sekuri
Noi Sekuri 2020-4-23
评论： Hank 2020-4-29
I want to plot three functions (x,y1) (x, y2) (x, y3) at the same graph. The point is that I want to be able to see the curve of xlogx function (I dont want to have a flat (x,y2) function) while the other two remain flat. How can I do this?
x values will be from 1000 to 24001000 and increse by 10000.
x = [1000, 1001000, 2001000, 3001000, 4001000, 5001000, 6001000, 7001000, 8001000, 9001000, 10001000, 11001000, 12001000, 13001000, 14001000, 15001000, 16001000, 17001000, 18001000, 19001000, 20001000, 21001000, 22001000, 23001000, 24001000]
y1 values will be 1000 times each corresponding x.
y2 values will be x * log(x) (base of logarithm will be 2)
y3 values will be just equal to each corresponding x value

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采纳的回答

Adam Danz
Adam Danz 2020-4-23
x * log(x) should be
x .* log(x)
% ^
and then set the y axis scale to log.
set(gca, 'YScale', 'log')
% Or, if you have the axis handle,
ax.YScale = 'log';
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Adam Danz
Adam Danz 2020-4-23
编辑：Adam Danz 2020-4-23
"I get a flat xlogx line with your solution. I want to have it curved and only the linear functions flat."
In that case, use the yyaxis solution I wrote above.
Put the linear lines on the left (or right) axis and the log line on the other axis. Then set the appropriate axis to log scale using the line of code from my answer. Just note that the two linear scaled lines are on vastly different sales so one of them will be at the bottom of the plot (see below).
If you run into problems, share your code so I can help straighten it out.

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更多回答（1 个）

Hank
Hank 2020-4-23
Your three function values fall in a range of orders of magnitude spanning 1e3 to 1e10. I think this code is the best visualization of the three functions in the same graph
x = (1000:1e5:24.001e6)'; % x values
% functions as you described
y1 = 1000*x;
y2 = x.*log(x);
y3 = x;
% plot(x,[y1 y2 y3]) %this doesn't work well because y2 and y3 appear near the x axis
semilogy(x,[y1 y2 y3]) % plots the three functions with a logscale y axis
  2 个评论
Noi Sekuri
Noi Sekuri 2020-4-23
Thank you but can I plot such that linear functions are flat and only xlogx function is curved? Your solution makes all of them curved.

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