plotting Formulas with greek letters and variable values (expression, substitute, paste, ...)

text(0,7.5,substitute(expression(paste(symbol("t"),"(A) = ",c1 +
lg(A^c2),sep="")),list(c1=0,456,c2=-0.123)),pos=4)

Hallo together,

I want to write a formula of the type

http://n4.nabble.com/file/n1016112/expression.gif







into my plot, where the values 1.234 and -0.567 should origin from variables
in the program. The threads in this forum gave me some ideas that the
functions expression(), paste(), and substitute() will get me there but I
just cannot figure out how to do it. The closest I got is:

text(0,7.5,substitute(expression(paste(symbol("t"),"(A) = ",c1 +
lg(A^c2),sep="")),list(c1=0,456,c2=-0.123)),pos=4)

Thankful for any suggestions!
Daniel
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I want to write a formula of the type

 http://n4.nabble.com/file/n1016112/expression.gif 

into my plot, where the values 1.234 and -0.567 should origin from
variables in the program.

It is much easier, just write the formula down in R syntax and 
substitute the relevant variables as in:

text(0, 7.5, substitute(tau(A) == a*lg(A^b), list(a=1.234, b=-0.567)))

Try bquote:

a <- 0.1; b <- 0.2
plot(0, main = bquote(tau(A) == .(a)*lg(A^.(b))))

suba <- 1.234; subb <- -0.567
text(0, 5,substitute(tau(A) == a*lg(A^b), list(a=suba, b=subb)),pos=4)  ##
and
text(0, 5,bquote(tau(A) == .(suba)*lg(A^.(subb))),pos=4)