29 Feb
                
                    2020
                
            
            
                29 Feb
                
                '20
                
            
            
            
        
    
                8:59 a.m.
            
        Hi Nacime, Thank you very much for your help. That solved the problem. The `float(alpha)/2` seems to be necessary. Regards N.B. There was missing "Placeholder(alpha)" and a minus sign in the previous code. I attached the working code for the record.