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How can I avoid 'and' in result? or any other way to solve

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Tarsem Singh Khalsa
Tarsem Singh Khalsa am 14 Apr. 2018
Geschlossen: MATLAB Answer Bot am 20 Aug. 2021
I'm writing a code for vibration of beam, the problem is that after derivation and substituting boundary values the result contains 'and' relation between two equation. It maybe due to the assumption, but it is necessary. Is there a way to avoid 'and' in this result?
BC: (for cantilever beam, beam length = 4m)
Y(x=0)=0
Y'(x=0)=0
Y''(x=4)=0
Y'''(x=4)=0
code:
Y=A*sin(b*x)+B*cos(b*x)+C*sinh(b*x)+D*cosh(b*x);
Yx=[1 0;1 0;0 1;0 1];
% Yx(i,j)=> i=n, (n-1)th derivative of Y
% j=1, at x=0; j=2, at x=Length of beam
assume(b>0);
t=0;
for i=1:4
for j=1:2
if Yx(i,j)==0
continue
end
t=t+1;
dY=diff(Y(x,b),x,(i-1));
F=simplify(expand(subs(dY,x,Yx(5,j))==0,'ArithmeticOnly',true));
c=symvar(F);
if or(size(c,2)==1,c(1)~='b')
d=1;
else
d=2;
end
if t==4;
assume(c(d)~=0)
Y=simplify(expand(F,'ArithmeticOnly',true));
else
G=solve(F,c(d));
Y(x,b)=subs(Y,c(d),G);
end
end
end
disp(Y);
The final result is like this:
Y = sin(4*b) + sinh(4*b) ~= 0 and cosh(4*b)^2 + 2*cos(4*b)*cosh(4*b) + 1 == sinh(4*b)^2
I'm using Matlab R2013a
  2 Kommentare
Walter Roberson
Walter Roberson am 14 Apr. 2018
You should be able to add an assume() that asserts the first relationship to be true and then it should simplify() out.
It does appear to be true for all positive b.
Tarsem Singh Khalsa
Tarsem Singh Khalsa am 15 Apr. 2018
Thanx that worked perfectly.

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