# Question:error message'' which is not valid for its 1st argument, expr''''

## Question:error message'' which is not valid for its 1st argument, expr''''

Maple 2016

hi

how i can remove this error?

1) ''Error, invalid input: lhs received diff(diff(diff(diff(w(x, y, t), x), x), x), x)+.12*(diff(diff(diff(diff(w(x, y, t), x), x), y), y))+0.11e-2*(diff(diff(diff(diff(w(x, y, t), y), y), y), y))+10-.4*(diff(diff(w(x, y, t), x), x))-0.4e-2*(diff(diff(w(x, y, t), y), y))+diff(diff(w(x, y, t), t), t)-w(x, y, t)-tau, which is not valid for its 1st argument, expr'''''

2)'' Error, incorrect number of extra arguments in select''

thanks > restart:Digits := 15: beta := 1: alpha := 0.1: Upsilon := .1: xi := 10: eta := .1: N_X := .4: N_Y := .4: psi: =4.73:  (1)
 >  (2)
 >  (3)
 >  (4)
 >

 > BC1:=subs(a=1,b=1,[BC]) (5)

We use the method of multiple scales to directly attack EOM1 and BC1. To transform the time derivatives in EOM1 in terms of the scales  and , we let

 > timeScales:=T,T (6) (7)
 > msForm:={w(x,y,t)=w(x,y,timeScales),seq(diff(w(x,y,t),t\$i)=dt[i](w(x,y,timeScales)),i=1..2)} (8)
 > multiScales:=`union`(map(s->subs(w=s,msForm),[w])[]) (9)

Then, we seek a second-order approximate solution in the form (10)

We introduce the detuning  to describe the nearness of the edge lengths  and , consider the case of primary resonance, and hence let

 > tau=epsilon^3*tau(x,y)*convert(cos(Omega*T),exp) (11)
 > Substituting multiScales, solRule, and scaleRule2 into EOM1, expanding the result for small , and discarding terms of order higher than , we obtain

 > expr83a:=seq(convert(series(value(subs(multiScales,solRule,lhs(EOM))),epsilon,4),polynom),i=1)  >   (12)  