Validating Decimal Numbers

Question

I have a form and I am using jQuery validation plugin to validate it. Now I am trying to validate decimal number input.

I have tried the following code, but its not working. Is the problem with the regular expression or the way of writing the custom rule is wrong in my code?

 rules: {
      paid_amount: {
              required:true,
                      rexp: ^[1-9]\d*(\.\d+)?$
      },

   }
     },

 messages: {
             paid_amount: {
                      required: "Enter Paid Amount",
              rexp:"Decimal Numbers Only"
    },  

     }
});