Illegal operation: log( {convex} ) how to deal with this kind of operation, please give me a favor

M=4;
K=10;
I=M+1;
cvx_begin
variables eta delta(M,1) xi(M,1)
expressions R1(M,K) R2(I,M) R3(M,K) R4(M,M)
maximize(eta)
subject to
%% first constraint
for m=1:M
for k=1:K
R1(m,k)=-(delta(m,1).^2+xi(m,1).^2)-delta(m,1)-xi(m,1);
end
sum(R1(m,:)) >= eta;
end
%% second constraint
for m=1:M
for i=1:I
R2(i,m)=-(square(delta(m,1))+square(xi(m,1)))-delta(m,1)-xi(m,1);
end
for k=1:K
R3(m,k)=log(pow_p((1+2*delta(m,1)+2.*xi(m,1)),-1))/log(2); % illegal operation here
end
for j=1:M
R4(m,j)=log(pow_p((1+2.*delta(m,1)+2.*xi(m,1)),-1))/log(2); % illegal operation here
end
sum(R2(:,m))>=sum(R3(m,:))+sum(R4(m,:));
end
cvx_end

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