Error using plot Vectors must be the same lengths

2013 4 12
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Hi,,
iam not matlab pro. :)
so i have problem on a very simple program
that's the program >>>>>>>>>>>>>>>>
vo=input('vo=');
vf=input('vf=');
to=input('to=');
tf=input('tf=');
qo=input('qo=');
qf=input('qf=');
ao=qo;
a1=diff(qo);
syms t;
syms dis;
a2=(3*(qf-qo)-(2*diff(qo)+diff(qf))*tf)/((tf)^2);
a3=(-2*(qf-qo)+(diff(qo)+diff(qf))*tf)/(tf)^3;
dis=ao+a1*t+a2*t^2+a3*t^3;
vel=a1+2*a2*t+3*a3*t^2;
acc=2*a2+6*a3*t;
t=0:tf;
plot(dis,t);
when i press play this error shown to me " Error using plot Vectors must be the same lengths "
so please how can i edit this program to playing well

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Walter Roberson
Walter Roberson 2013-4-12

0 个投票

ndis = double( subs(dis, 't', t) );
plot(ndis, t);

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koke
koke 2013-4-12
tahnx for your interest but that's doesn't solving the problem it's still give me the same error after i adding your solution best regard :)
Walter Roberson
Walter Roberson 2013-4-12
What does size(ndis) and size(t) show ?
koke
koke 2013-4-12
ndis 0*0 double t 1*11 double
Walter Roberson
Walter Roberson 2013-4-12
编辑：Walter Roberson 2013-4-12
Could you show us what "dis" is before the plot?
What exactly are you entering in response to the prompt for qo ?
koke
koke 2013-4-12
编辑：koke 2013-4-12
the input of qo is = 10
Walter Roberson
Walter Roberson 2013-4-12
if q0 is 10, then what are you expecting the result of diff(q0) to be ?
Walter Roberson
Walter Roberson 2013-4-12
diff() of a scalar numeric value is [] the empty list, because diff() of numerics is the subtract-adjacent operation.
If q0 had been assigned the symbolic value 0, sym('0') then diff() of that would likely generate an error because there would not be any variable contained inside it for the symbolic calculus differential operator to choose to take the differential with respect of.
If you had specified a variable, such as diff(sym('0'), sym('t')) then the result would be (symbolic) 0.
Likewise for the other variables you are taking diff() of. It does not seem productive to bother to use diff() to calculate what you know will be 0... unless you are wanting the user to be able to enter NaN in which case the calculus differential would be NaN instead of 0.

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