Error Using Interp1

I am new to MATLAB I am trying to run a simple code but keep getting the following error:

Error using griddedInterpolant/subsref Invalid arguments specified in evaluating the interpolant.

Error in interp1 (line 151) VqLite = F(Xqcol);

Error in test34 (line 13) Gp1BexC2H6-((1/22.6127535749917)*250*(interp1(x_data_C2H6,y_data_C2H6,vq)))==0;

the script is as follows

Methane_40C = [49.9250000000000,3.41300000000000;48.1190000000000,3.47400000000000;46.1580000000000,3.53100000000000;44.2580000000000,3.58900000000000;41.9420000000000,3.68100000000000;38.0910000000000,3.83700000000000;36.0150000000000,3.96900000000000;34.0170000000000,4.08100000000000;32.0230000000000,4.24200000000000;30.1820000000000,4.38300000000000;28.0730000000000,4.58000000000000;26.0850000000000,4.78700000000000;24.0580000000000,5.00300000000000;21.9750000000000,5.22600000000000;17.8660000000000,5.71700000000000;16.0030000000000,5.96400000000000;14.0790000000000,6.16800000000000;12.0840000000000,6.34800000000000;9.81600000000000,6.47500000000000;7.91300000000000,6.45200000000000;6.03300000000000,6.29700000000000;5.13300000000000,6.12300000000000;4.06100000000000,5.87900000000000;3.05000000000000,5.43600000000000;1.91900000000000,4.62500000000000;0.739000000000000,3.14900000000000;0.0310000000000000,0.997000000000000]; Ethane_40C = [[49.9960000000000,1.58400000000000;46.9420000000000,1.62100000000000;43.4100000000000,1.64400000000000;40.3150000000000,1.69600000000000;37.6160000000000,1.73900000000000;35.2460000000000,1.78600000000000;32.5590000000000,1.83400000000000;30,1.88200000000000;27.7270000000000,1.93700000000000;25.1650000000000,2.01900000000000;22.6710000000000,2.10900000000000;20.3830000000000,2.18400000000000;18.2300000000000,2.27200000000000;16.4810000000000,2.36900000000000;14.8120000000000,2.45900000000000;13.0290000000000,2.58600000000000;11.4070000000000,2.75400000000000;10.3070000000000,2.88200000000000;9.12600000000000,3.06700000000000;6.99500000000000,3.69000000000000;5.93000000000000,4.77100000000000;4.11100000000000,7.29300000000000;3.07900000000000,7.49600000000000;2.06100000000000,7.40600000000000;1.05400000000000,6.72100000000000;0.185000000000000,4.73300000000000]]; x_data_CH4=Methane_40C(:,1); y_data_CH4=Methane_40C(:,2); x_data_C2H6=Ethane_40C(:,1); y_data_C2H6=Ethane_40C(:,2);

Ptot1B==12; y1BCH4=2; vq==((1-y1BCH4)*Ptot1B); vq2==((y1BCH4)*Ptot1B);

Gp1BexC2H6-((1/22.6127535749917)*250*(interp1(x_data_C2H6,y_data_C2H6,vq)))==0; Gp1BexCH4-(((1/42.3918640897756)*250*(interp1(x_data_CH4,y_data_CH4,vq2))))==0;

Answer 1

[Walter Roberson]

Ptot1B==12; y1BCH4=2; vq==((1-y1BCH4)*Ptot1B); vq2==((y1BCH4)*Ptot1B);

Notice most of those are not assignment statements. You compare variables to something and throw away the results of the comparison.