1. A method of controlling a robot including processing information wherein, in a model in which restrictions among parameters are given by simultaneous algebraic equations with integral coefficients when the simultaneous equations have only a finite number of solutions, zero points of a polynomial set F with integral coefficients, which represents the simultaneous equations and is described in a memory, are represented by rational expressions based on zero points of a one-variable polynomial so that the information is processed using the representation of rational expressions the method comprising: 1-1. choosing a term order o.sub.1 for facilitating the calculation of the Grobner basis, 1-2. calculating the Grobner basis G.sub.1 of F with regard to o.sub.1, 1-3. calculating the minimum polynomial f.sub.1 based on G.sub.1, the minimum polynomial f.sub.1, being a polynomial having the minimum degree of the variable x.sub.1, 1-4. when it is decided that the degree of f.sub.1 (x.sub.1) is equal to the number of solutions given from G.sub.1, 1-5. controlling a digital processor to find solutions represented by rational expressions {f.sub.1 (X.sub.1)=o, X.sub.2 =f.sub.2 (X.sub.1)/f'.sub.1 (X.sub.1),. .. , X.sub.n =f.sub.n (X.sub.1)/f'.sub.1 (x.sub.1)}, wherein f'.sub.1 (x.sub.1) is differential of f.sub.1 (x.sub.1); and controlling the robot by using the solutions of the rational expressions.