Beginner - stuck on Matlab

1 次查看（过去 30 天）
Dominic
Dominic 2013-3-25
It's a question on MatLab Integration program, but have a look at this code first. It's a part of the Integration on Rectangle Method program:
[LINES 1-3]
x = 1 : 2 : 5; % x=lower limit: strip width: upper limit
% These are not supposed to be constants, but for this question's simplicity, let's keep it that way.
[LINE 4]
y_x = input ( 'Enter your function of x = ' )
% allowing the user to modify the function as required
[LINE 5]
S = 2 .* ( sum (abs (y_x)) )
Now, that works fine with the subsequent lines to calculate the approximation of the integration; but, I want what was input by the user for y_x to be also used for the plot TITLE, DISP, and others. The issue is y_x turns to an array instantly. If I turn the input into string [Ex: y_x = input ( ' Enter you function of x = ' , 's') ], it works with the DISP and TITLE, but it doesn't process the x array, so I don't get the integration approximation. Example, say x.^2 was input. Hence, y_x = x.^2
[LINE 6 - 7]
plot( x , y_x)
title(['Numeric Integration for' , num2str(y_x) , 'with 2 slices')
Instead of title being 'Numeric Integration for x.^2 with 2 slices', what shows is 'Numeric Integration for 1 9 25 with 2 slices.' [1 9 25] is the squares for x=1 : 2 : 5. That's because the input has turned to an array and info is lost. Anyone knows how to get around this problem?
Another problem is I also want the equation to be used on the FOR function:
for x = 1 : 2 : 5
y_x = ??? (something to go through the array and produce an array of y_x)
plot( [x x], [0 y_x])
end
That FOR function is to make vertical lines from the x-axis to the coordinate (x, y_x).
Thanks a lot!

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采纳的回答

Walter Roberson
Walter Roberson 2013-3-25
y_xs = input('Enter your function of x =', 's');
y_x = str2func( ['@(x) ', y_xs] );
Now, to calculate,
y_x(x)
and include y_xs in the title

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