Hi, I wanted to define a simple matrix of derivatives (i.e: a Jacobian) first as an indexed object: ex f = a*x + b*y + c*x*y + ... ex g = u*pow(x,2) + v*pow(y,2) + w*x,y + .... idx i(symbol("is") , 2) , j(symbol("js") , 2); ex Jacobian = diff( f*delta_tensor(i , 0) + g*delta_tensor(i,1) , x )*delta_tensor( 0 , j ) + diff( f*delta_tensor(i , 0) + g*delta_tensor(i,1) , y )*delta_tensor( 1 , j ); but then this failed on me (because 0 and 1 are not acceptable arguments where an idx should be expected) Why am i trying to do this as an indexed object and not with a matrix? well, because later, i would also want to make computations with an object like D( f_{i} ) / dx_{j} dx_{k} but afaik there isnt a "three indexed" matrix object in ginac, or how they are usually called, cubic arrays. correct? __________________________________________________ Preguntá. Respondé. Descubrí. Todo lo que querías saber, y lo que ni imaginabas, está en Yahoo! Respuestas (Beta). ¡Probalo ya! http://www.yahoo.com.ar/respuestas