Error when solving an equation involving a poisson pdf

Hello, I am trying to find for what values of lambda P(X=10) = 0.1, if X~Po(lambda)

My code is:

syms lambda

solve(poisspdf(10,lambda)==0.1, lambda)

the error I get is:

'error using symengine. Unable to prove 'lambda<0' literally . Use 'isAlways to test the statement mathematically

any help would be much appreciated!

Answer 1

[Star Strider]

Try this (instead of using the Symbolic Math Toolbox):

lambda = fzero(@(lambda) poisspdf(10, lambda) - 0.1, 5)

producing:

lambda =
     8.0299

[Louis Sharma]

Thanks this is great! By looking at my plot, I see that there are 2 solutions to this equation (I selected lambda=0:1:20). Any idea how I could get the second solution?

Thank you so much!

[Louis Sharma]

actually I was able to ge the second solution by changing the range. Thanks

[Star Strider]

As always, my pleasure!

(I was sleeping, not ignoring you!)