Error estimation of fitting parameters

 https://stackoverflow.com/questions/40187517/getting-covariance-matrix-of-fitted-parameters-from-scipy-optimize-least-squares

PyQt5 adding FigureCanvas in designer

(1) Put a layout in a designer. rename it as convenient

(2) Click Right Mouse Button and change it into a Widget. 

(3) After that, one can put Canvas Widget into the layout.