how to calculate a derivative

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Nasir Qazi
Nasir Qazi 2012-2-26
评论： Steven Lord 2025-5-12
can some one guide me how to calculate a derivative and integration in matlab . can you please give a little example.

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采纳的回答

bym
bym 2012-2-26
Symbolically
syms x real
f = 1/x
int(f,1,2) % integration
ans =
log(2)
diff(f) %differentiation
ans =
-1/x^2
[edit - amplification]
syms x a b real positive
f = 1/x
f =
1/x
int(f) % without limits
ans =
log(x)
int(f,a,b) % with limits
ans =
log(b) - log(a)
fn = matlabFunction(f) % convert symbolic to anonymous function
fn =
@(x)1./x
quadgk(fn,1,2) % integrate numerically
ans =
0.6931
log(2) % previous result from symbolic integration
ans =
0.6931
(fn(2+1e-6)-fn(2))/1e-6 %numerical derivative at fn(2)
ans =
-0.2500
subs(diff(f),2) %substitute 2 into symbolic result previously obtained
ans =
-0.2500
  5 个评论
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Jan
Jan 2012-2-27
Yes, Nasir, then the integral is calculated from 1 to 2. "Symbolically" mean calculations with symbols, usually characters. The result is a formula. "Numerically" means, that you calculate a numerical value, a number.
Sergio E. Obando
Sergio E. Obando 2024-6-15
Just here to suggest some recent resources, There is a nice section in the Symbolic Math Toolbox with additional examples for differentiation as well as a FEX curriculum on this topic:

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更多回答（3 个）

Magdalena Glinska
Magdalena Glinska 2020-11-16
f = @(x) sin(x);
second_derivative_f = matlabFunction(diff(sym(f)));
Hamza saeed khan
Hamza saeed khan 2020-11-24
syms x
f = x;
diff(f,x)
why this code give me error as;
>>Error in diff (line 1)
syms x
  4 个评论
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belvia
belvia 2025-5-12

même chez moi le diff là ne donne pas

Steven Lord
Steven Lord 2025-5-12
"même chez moi le diff là ne donne pas"
Please show us the exact code you're running and all the text displayed in red in the Command Window (and if there are any warning messages displayed in orange, please show us those too) that you see when you run that code. The exact text may be useful and/or necessary to determine what's going on and how to avoid the warning and/or error.

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Achimsettythanmay
Achimsettythanmay 2022-11-14
编辑：Walter Roberson 2022-11-15
Ran in:
syms x real
f = 1/x
f = 
int(f,1,2) % integration
ans = 
diff(f) %differentiation
ans = 

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