Inconsistency between sizes of second and third arguments

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Pranav
Pranav 2023-1-13
回答： Piyush Patil 2023-3-3
Hi, I am getting an error while calculating work done with a given vector and parameter. How to rectify that?
F=subs(f,{x,y},r); % Inconsistency between sizes of second and third arguments
Fdr=sum(F.*dr); % [X2,Y2,symX,symY] = normalize(X,Y);
% My code is below:
clc
clear all
syms x y t
f=input('Enter the components of 2D vector function [u,v] ');
r=input('Enter x,y in parametric form');
I=input('Enter the limits of integration for t in the form [a,b]');
a=I(1);b=I(2);
dr=diff(r,t);
F=subs(f,{x,y},r);
Fdr=sum(F.*dr);
I=int(Fdr,t,a,b)
P(x,y)=f(1);Q(x,y)=f(2);
x1=linspace(-2*pi,2*pi,10); y1=x1;
[X,Y] = meshgrid(x1,y1);
U=P(X,Y); V=Q(X,Y);
quiver(X,Y,U,V,1.5)
hold on
t1=linspace(0,2*pi);
x=subs(r(1),t1);y=subs(r(2),t1);
plot(x,y,'r')
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Pranav
Pranav 2023-1-13
yeah, sure!
f = [(x^2) (y^2)]
r = [2*(x^2)] from (-1,2) to (2,8)
Dyuman Joshi
Dyuman Joshi 2023-1-13
You are trying to substitute 2 values but input is only single value.
Also, (-1,2) to (2,8) is input to I?

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回答（1 个）

Piyush Patil
Piyush Patil 2023-3-3
Hello Pranav,
You are getting an error because the input vector for the 2D vector function f is not of the same size as that of the input vector for r.
In your case, f has two components, so it is a 1x2 vector, while r has only one component, so it is a scalar.
In order to resolve this error, you can rewrite the parametric curve r in terms of t only.
For example, consider the vector function f = [x^2 y^2] over the parametric curve r = [2*(t^2) 4*(t^2)] where the limits of integration for t are [-4 4]
syms x y t
f = input('Enter the components of 2D vector function [u,v]: ');
r = input('Enter x,y in parametric form [x(t),y(t)]: ');
I = input('Enter the limits of integration for t in the form [a,b]: ');
a = I(1)
b = I(2)
dr = diff(r, t)
F = subs(f, {x,y}, r)
Where your inputs are -
f = [x^2 y^2]
r = [2*(t^2) 4*(t^2)]
I = [-4 4]

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