graph of differenc equation

sketching the graph of the equation(which circle it in first image ) for( f) with all parameters ( a ,alpha one ,alpha two, mu one, sigma) by using wolfram Alpha program . (f)should be always in the x axis(you should write F in the graphs) , and all parameters in y axis (you should write them in graphs) . I want just positive side from axis in the all graphs expect sigma I want two sides. I want the picture of graph big enough not small. there are some examples of the graphs I included in files . it will be very similar. make sure you take small values for alpha to get perfect graph.