Hi I give you an example. If you run the following lines in maple you will get a tensor ******************** A:=array(1..3,1..3,[[a,0,0],[0,a,0],[0,0,a]]): tensor[create]([-1,-1],eval(A) ); ************************ However if you run ir in maplet you recieve the Evaluate_result message.have a go: ******************************** with(Maplets[Elements]): maplet := Maplet( Window( 'title'="test", [ ["g_compts ", TextField['TF1'](( 'value' = array(1..3,1..3,[[a,0,0],[0,a,0],[0,0,a]]),60))], TextBox['TB1']('editable' = 'true', 3..40 ), [Button("create tensor", Evaluate('TB1' = 'tensor[create]([-1,-1],eval(TF1) )' )), Button("OK", Shutdown(['TF1', 'TB1']))] ] ) ): Maplets[Display]( maplet ); ******************************************* The problem is that you can not create tensors in maplet! hossein

Hi I give you an example. If you run the following lines in maple you will get a tensor ******************** A:=array(1..3,1..3,[[a,0,0],[0,a,0],[0,0,a]]): tensor[create]([-1,-1],eval(A) ); ************************ However if you run ir in maplet you recieve the Evaluate_result message.have a go: ******************************** with(Maplets[Elements]): maplet := Maplet( Window( 'title'="test", [ ["g_compts ", TextField['TF1'](( 'value' = array(1..3,1..3,[[a,0,0],[0,a,0],[0,0,a]]),60))], TextBox['TB1']('editable' = 'true', 3..40 ), [Button("create tensor", Evaluate('TB1' = 'tensor[create]([-1,-1],eval(TF1) )' )), Button("OK", Shutdown(['TF1', 'TB1']))] ] ) ): Maplets[Display]( maplet ); ******************************************* The problem is that you can not create tensors in maplet! hossein

Hi Alec when I looked at your solution carefully I realised that the one displayed in MathMLviewer is not a tensor. in fact by executing the following lines in maple > with(tensor): > g_compts:=array(symmetric,sparse,1..4,1..4): > g_compts[1,1]:=(1-2*m/r): g_compts[2,2]:=-1/g_compts[1,1]: > g_compts[3,3]:=-r^2: g_compts[4,4]:=-r^2*sin(th)^2: > g:=create([-1,-1], eval(g_compts)); we see that the tensor is TABLE([compts = matrix([[1-2*m/r, 0, 0, 0], [0, -1/(1-2*m/r), 0, 0], [0, 0, -r^2, 0], [0, 0, 0, -r^2*sin(th)^2]]), index_char = [-1, -1]]) which is different from yours. The difference is that the whole thing is inside a 'TABLE[]'.Then is become a tensor. I need that to be a tensor because i need it in the later steps. Now please help me with this one. Thanks in advance. Regards Hossein

thanks very much, Alex. that was what I really needed.

More generally, I would like to create a maplet that by giving a seconf rank covaiant metric the user can get different genral relativity objects. At the first step, say I enter an array in the maplet in a textbox and then creating a metric via the Evaluate command. This can not be done in maplet. (notable that I only found examples of maplets that evaluates integrals or derivalites). for example: I need to enter the metric componenets as follows g_compts:=array(symmetric,sparse,1..4,1..4): g_compts[1,1]:=(1-2*m/r): g_compts[2,2]:=-1/g_compts[1,1]: g_compts[3,3]:=-r^2: g_compts[4,4]:=-r^2*sin(th)^2: and need to create and display the metric by using the code g:=create([-1,-1], eval(g_compts)); How this in Maplet?! regards Hossein