function [s, lowercrossvalue, uppercrossvalue, lowerreference, upperreference]=slewrate(x, varargin)


    // This function estimate slew rate of bilevel waveform transitions
    // Calling Sequence
    // s=slewrate(x)
    // s=slewrate(x, t)
     // s=slewrate(x, Fs)
    // s=slewrate(x, t, 'PercentReferenceLevels', N )
    // s=slewrate(x, t, 'Tolerance', M)
    // s=slewrate(x, t,'StateLevels', O)

    // [s lowercrossvalue uppercrossvalue lowerreference upperreference]=slewrate(x)
    // [s lowercrossvalue uppercrossvalue lowerreference upperreference]=slewrate(x, t)
    // // [s lowercrossvalue uppercrossvalue lowerreference upperreference]=slewrate(x, Fs)
    // [s lowercrossvalue uppercrossvalue lowerreference upperreference]=slewrate(x, t, 'PercentReferenceLevels', N )
    // [s lowercrossvalue uppercrossvalue lowerreference upperreference]= slewrate(x, t, 'Tolerance', M)
    // [s lowercrossvalue uppercrossvalue lowerreference upperreference]= slewrate(x, t,'StateLevels', O)
    // [s lowercrossvalue uppercrossvalue lowerreference upperreference]= slewrate(x, t,'StateLevels', O, 'fig', on or off)
    //
    // Parameters
    // x: real vector.
    // Fs: specifies the sample rate, Fs, as a positive   scalar, where the first sample instant corresponds to a time of zero.
    // t: defiene instant sample time t as vector with same length of x, or specifies the sample rate, t, as a positive scalar.
    // PercentReferenceLevels: specify the mid percent reference leves as a percentage, default value of N is [10 90].
    // Tolerance: define the tolerance value as real scaler value, where default value of M is 2.0.
    // StateLevels:  define the lower and upper state levels as two element real vector.
    // fig: specify the logical input value to display figure as one of 'on' or 'off', where the default input in 'off'.
    // s: returns a vector of the ratios of the level difference to the time duration between the points where each transition crosses the 10% and 90% reference levels.
    // lowercrossvalue: return the lowerc cross value of bilevel waveform transitions X
    // uppercrossvalue: return the upper cross value of bilevel waveform transitions X
    // lowerreference: return lower reference value corrosponding to lower percent reference value.
    // upperreference: return upper reference value corrosponding to upper percent reference value.

    // Example1
    // x=[1.2, 5, 10, -20, 12]
    //t=1:length(x)
    //s=slewrate(x, t)
    //EXPECTED OUTPUT:
    //s  = - 30.    32.
    //
    //Example2
    //x=[ones(1,25)  -ones(1,25)  ones(1,25) ]
    //t=1:length(x)
    //s=slewrate(x,t)
   //EXPECTED OUTPUT:
    //s  = - 2  2

    // See also
    // Authors
    // Jitendra Singh


  // run statelevels and midcross function before running risetime function.

         if or(type(x)==10) then
    error ('Input arguments must be double.')
end

if size(x,1)==1 | size (x,2)==1 then
    else
    error ('Argument X must be vector.')
end



   if  length(varargin)==0 then  // if the no of input is 0, then specify the default values to input parameter.
        [levels hist]=statelevels(x);
        Lvarargin=list(1:length(x), 'StateLevels', levels(1), 'MidPercentReferenceLevel', 10, 'Tolerance', 2, 'fig', 'off')
        Uvarargin=list(1:length(x), 'StateLevels', levels(2), 'MidPercentReferenceLevel', 90, 'Tolerance', 2, 'fig', 'off')
    end

if length(varargin)>=1 & type(varargin(1))==1 then
     if length(varargin(1))==1 then
        t=(0:(length(x)-1));

    elseif length(varargin(1))==length(x) then
        t=varargin(1);

    else
        error('T must be a same length as X.')
    end
else
    t=1:length(x);
end


if length(varargin)>=2 & type(varargin(1))==1 & type(varargin(2))==1 then
    error ("Too many leading numeric arguments (at most 2 expected).");
end




sindex=[];
if length(varargin)>=1 then
a=1;

for i=1:length(varargin)
    if type(varargin(i))==10 then
        sindex(a)=i;
        a=a+1;
        end
end
end


if length(sindex)>5 then
    error('Unexpected argument.')
end

if length(varargin)==1 & (isempty(sindex)) then

    [levels hist]=statelevels(x);
        Lvarargin=list(t, 'StateLevels', levels(1), 'MidPercentReferenceLevel', 10, 'Tolerance', 2, 'fig', 'off')
        Uvarargin=list(t, 'StateLevels', levels(2), 'MidPercentReferenceLevel', 90, 'Tolerance', 2, 'fig', 'off')

end

fig='OFF';
//////////////////////////////////

if (~isempty(sindex)) then
        for j=1:length(sindex)

            select convstr(varargin(sindex(j)),'u')

                case {'STATELEVELS'}
                   ////
                 if length(varargin) <=sindex(j) then
                      error(strcat(['parameter StateLevels required a value']));
                  end

                  if type(varargin(sindex(j)+1))==1 then
                      levels=varargin(sindex(j)+1);

                   elseif type(varargin(sindex(j)+1))==10 & convstr(varargin(sindex(j)+1), 'u')=='PERCENTREFERENCELEVELS' |  convstr(varargin(sindex(j)+1),'u')== 'TOLERANCE' | convstr(varargin(sindex(j)+1), 'u')=='FIG' then

                    error('parameter StateLevels required a value.')


                  elseif type(varargin(sindex(j)+1))==10  then

                    error('Expected STATELEVELS to be one of these types: double, Instead its type was char.')
                    end


                case {'PERCENTREFERENCELEVELS'}
            if length(varargin) <=sindex(j) then
                      error(strcat(['parameter MidPercentRefernceLevel required a value.']));
                  end

                  if  type(varargin(sindex(j)+1))==1 then
                      midpercentval= varargin(sindex(j)+1);
                        elseif type(varargin(sindex(j)+1))==10 & convstr(varargin(sindex(j)+1), 'u')=='STATELEVELS' | convstr(varargin(sindex(j)+1),'u')== 'TOLERANCE' | convstr(varargin(sindex(j)+1), 'u')=='FIG' then
                    error('parameter MidPercentRefernceLevel required a value.')

                  elseif type(varargin(sindex(j)+1))==10 then
                    error('Expected MidPercentRefernceLevel to be one of these types: double, Instead its type was char.')
                end

                if length( midpercentval)~=2 then
                    error ('Expected MidPercentRefernceLevel to be of size 1x2')
                end
  /////////////////////////////////

                    perval=varargin(sindex(j)+1);
                    disp(perval)
                   if perval(2)<= perval(1) then
                     error('The PercentReferenceLevels must be in increasing order.')
                     end

                       varargin(sindex(j))='MidPercentReferenceLevel';
                     varargin(sindex(j)+1)=perval(1);
                    Lvarargin= varargin;

                    varargin(sindex(j)+1)=perval(2);
                    Uvarargin=varargin;



            case {'FIG'}

                if length(varargin) <=sindex(j) then
                      error(strcat(['parameter fig required a value.']));
                  end

                  if type(varargin(sindex(j)+1))==1 then
                      error ('Expected fig to match one of these strings: on or off');

                 elseif type(varargin(sindex(j)+1))==10 & convstr(varargin(sindex(j)+1), 'u')=='STATELEVELS' | convstr(varargin(sindex(j)+1), 'u')== 'TOLERANCE' | convstr(varargin(sindex(j)+1), 'u')=='PERCENTREFERENCELEVELS' then
                    error('parameter fig required a value.')
                    else
                        fig=  convstr(varargin(sindex(j)+1), 'u');

                    end


                     if fig == 'OFF' | fig == 'ON' then
        else
     error('Expected fig to match one of these strings: on or off');
           end



        case{'ON'}



         case{'OFF'}


                case {'TOLERANCE'}

            if length(varargin) <=sindex(j) then
                      error(strcat(["parameter Tolerance required a value"]));

                  elseif type(varargin(sindex(j)+1))==1 then
                     tolerance= varargin(sindex(j)+1);

                  elseif type(varargin(sindex(j)+1))==10 & convstr(varargin(sindex(j)+1), 'u')== 'STATELEVELS' | convstr(varargin(sindex(j)+1), 'u')== 'PERCENTREFERENCELEVELs' | convstr(varargin(sindex(j)+1), 'u')=='FIG' then

                    error('parameter Tolerance required a value.');

                  elseif type(varargin(sindex(j)+1))==10  then

                    error('Expected Tolerance to be one of these types: double, Instead its type was char.');
                    end


            else
              error(strcat(['Invalid optional argument'," ", varargin(sindex(j))]));
            end // switch
        end // for
    end // if

/////////////////////////////////////////////



 indexx=[];
if length(sindex)>=1  then
a=1;
for i=1:length(sindex)

  indexx(a)=find(convstr(varargin(sindex(i)), 'u')=='MIDPERCENTREFERENCELEVEL')
    a=a+1;
end
end


if  sum(indexx)==0 then

     varargin(length(varargin)+1)='MIDPERCENTREFERENCELEVEL';
           varargin(length(varargin)+1)=10;
                    Lvarargin= varargin;

                    varargin(length(varargin))=90;
                    Uvarargin=varargin;
end

index_on=[];

if length(sindex)>=1  then
a=1;

for i=1:length(sindex)

  index_on(a)=find(convstr(varargin(sindex(i)), 'u')=='ON')

    a=a+1;

end
end

if sum(index_on)>0 then
    Lvarargin(sindex(find(index_on>0)))='OFF';
    Uvarargin(sindex(find(index_on>0)))='OFF';
end




   [lcrossval lref levels t tolerance]= midcross(x, Lvarargin(:));

    [ucrossval uref]=midcross(x, Uvarargin(:));


    if length(lcrossval)==length(ucrossval) then
        ss=ucrossval-lcrossval

    elseif length(lcrossval)>length(ucrossval)
        n=length(ucrossval);
       ss=ucrossval-lcrossval(1:n);

    else
        n=length(lcrossval);
        ss=ucrossval(1:n)-lcrossval;


 end


 s=(uref-lref)./ss;


 uppercrossvalue=ucrossval;
 lowercrossvalue=lcrossval;

 lowerreference=lref;
 upperreference=uref;

     upperbound= levels(2)- (tolerance/100)*(levels(2)-levels(1));
 mostupperbound=levels(2)+ (tolerance/100)*(levels(2)-levels(1));
  lowerbound= levels(1)+ (tolerance/100)*(levels(2)-levels(1));
  mostlowerbound=levels(1)- (tolerance/100)*(levels(2)-levels(1));





   if fig=='ON' then   // if the defined output is only 1, the it will provide the graphical representation of                          //levels

      if length(s)==0 then

        plot(t,x, 'LineWidth',1, 'color', 'black')

         plot(t,upperreference * ones(1, length(t)),'-r', 'LineWidth',0.5)

       plot(t,lowerreference * ones(1, length(t)),'-g', 'LineWidth',0.5)


      plot(t,mostupperbound * ones(1, length(t)),'--r', 'LineWidth',0.5)

      plot(t,levels(2) * ones(1, length(t)),'--k', 'LineWidth',0.5)

      plot(t,upperbound * ones(1, length(t)),'--r', 'LineWidth',0.5)



       plot(t,lowerbound *ones(1, length(t)),'--g', 'LineWidth',0.5)

       plot(t,levels(1) * ones(1, length(t)),'--k', 'LineWidth',0.5)

       plot(t,mostlowerbound * ones(1, length(t)),'--g', 'LineWidth',0.5)

       xlabel("Time (second)", "fontsize",3, "color", "black" )
     ylabel("Level (Volts)", "fontsize",3, "color", "black" )


     legends(["Signal";   "upper boundary"; "upper state"; "lower boundary"; "upper reference"; "lower reference"; "upper boundary"; "lower state"; "lower boundary"],  [[1;1], [5;2], [1;2], [5;2], [5;1], [3;1], [3;2], [1;2], [3;2]], opt='?')


      else


      plot(t,x, 'LineWidth',1, 'color', 'black')

       plot(t,upperreference * ones(1, length(t)),'-r', 'LineWidth',0.5)

      plot(t,lowerreference * ones(1, length(t)),'-g', 'LineWidth',0.5)

    rects=[lowercrossvalue; upperreference*ones(lowercrossvalue); ss; (upperreference-lowerreference)*ones(s)]

   col=-10*ones(s);

    xrects(rects, col);

     plot(uppercrossvalue, upperreference*ones(uppercrossvalue), "r*", 'MarkerSize',15);

      plot(lowercrossvalue, lowerreference*ones(lowercrossvalue), "g*", 'MarkerSize',15);

      plot(t,mostupperbound * ones(1, length(t)),'--r', 'LineWidth',0.5)

      plot(t,levels(2) * ones(1, length(t)),'--k', 'LineWidth',0.5)

      plot(t,upperbound * ones(1, length(t)),'--r', 'LineWidth',0.5)



       plot(t,lowerbound *ones(1, length(t)),'--g', 'LineWidth',0.5)

       plot(t,levels(1) * ones(1, length(t)),'--k', 'LineWidth',0.5)

       plot(t,mostlowerbound * ones(1, length(t)),'--g', 'LineWidth',0.5)
//
       xlabel("Time (second)", "fontsize",3, "color", "black" )
     ylabel("Level (Volts)", "fontsize",3, "color", "black" )


     legends(["slewrate"; "Signal"; "upper cross"; "lower cross"; "upper boundary"; "upper state"; "lower boundary"; "upper reference"; "lower reference"; "upper boundary"; "lower state"; "lower boundary"],  [[-11; 2] , [1;1], [-10;5], [-10;3], [5;2], [1;2], [5;2], [5;1], [3;1], [3;2],[1;2], [3;2]], opt='?')

   end
   end


endfunction